Continuous Maps Between Topological Manifolds¶
ContinuousMap implements continuous maps from a topological
manifold \(M\) to some topological manifold \(N\) over the same topological
field \(K\) as \(M\).
AUTHORS:
- Eric Gourgoulhon, Michal Bejger (2013-2015): initial version 
- Travis Scrimshaw (2016): review tweaks 
REFERENCES:
- class sage.manifolds.continuous_map.ContinuousMap(parent, coord_functions=None, name=None, latex_name=None, is_isomorphism=False, is_identity=False)[source]¶
- Bases: - Morphism- Continuous map between two topological manifolds. - This class implements continuous maps of the type \[\Phi: M \longrightarrow N,\]- where \(M\) and \(N\) are topological manifolds over the same topological field \(K\). - Continuous maps are the morphisms of the category of topological manifolds. The set of all continuous maps from \(M\) to \(N\) is therefore the homset between \(M\) and \(N\), which is denoted by \(\mathrm{Hom}(M,N)\). - The class - ContinuousMapis a Sage element class, whose parent class is- TopologicalManifoldHomset.- INPUT: - parent– homset \(\mathrm{Hom}(M,N)\) to which the continuous map belongs
- coord_functions– dictionary of the coordinate expressions (as lists or tuples of the coordinates of the image expressed in terms of the coordinates of the considered point) with the pairs of charts- (chart1, chart2)as keys (- chart1being a chart on \(M\) and- chart2a chart on \(N\))
- name– (default:- None) name given to- self
- latex_name– (default:- None) LaTeX symbol to denote the continuous map; if- None, the LaTeX symbol is set to- name
- is_isomorphism– boolean (default:- False); determines whether the constructed object is a isomorphism (i.e. a homeomorphism). If set to- True, then the manifolds \(M\) and \(N\) must have the same dimension.
- is_identity– boolean (default:- False); determines whether the constructed object is the identity map. If set to- True, then \(N\) must be \(M\) and the entry- coord_functionsis not used.
 - Note - If the information passed by means of the argument - coord_functionsis not sufficient to fully specify the continuous map, further coordinate expressions, in other charts, can be subsequently added by means of the method- add_expr().- EXAMPLES: - The standard embedding of the sphere \(S^2\) into \(\RR^3\): - sage: M = Manifold(2, 'S^2', structure='topological') # the 2-dimensional sphere S^2 sage: U = M.open_subset('U') # complement of the North pole sage: c_xy.<x,y> = U.chart() # stereographic coordinates from the North pole sage: V = M.open_subset('V') # complement of the South pole sage: c_uv.<u,v> = V.chart() # stereographic coordinates from the South pole sage: M.declare_union(U,V) # S^2 is the union of U and V sage: xy_to_uv = c_xy.transition_map(c_uv, (x/(x^2+y^2), y/(x^2+y^2)), ....: intersection_name='W', ....: restrictions1=x^2+y^2!=0, ....: restrictions2=u^2+v^2!=0) sage: uv_to_xy = xy_to_uv.inverse() sage: N = Manifold(3, 'R^3', latex_name=r'\RR^3', structure='topological') # R^3 sage: c_cart.<X,Y,Z> = N.chart() # Cartesian coordinates on R^3 sage: Phi = M.continuous_map(N, ....: {(c_xy, c_cart): [2*x/(1+x^2+y^2), 2*y/(1+x^2+y^2), (x^2+y^2-1)/(1+x^2+y^2)], ....: (c_uv, c_cart): [2*u/(1+u^2+v^2), 2*v/(1+u^2+v^2), (1-u^2-v^2)/(1+u^2+v^2)]}, ....: name='Phi', latex_name=r'\Phi') sage: Phi Continuous map Phi from the 2-dimensional topological manifold S^2 to the 3-dimensional topological manifold R^3 sage: Phi.parent() Set of Morphisms from 2-dimensional topological manifold S^2 to 3-dimensional topological manifold R^3 in Category of manifolds over Real Field with 53 bits of precision sage: Phi.parent() is Hom(M, N) True sage: type(Phi) <class 'sage.manifolds.manifold_homset.TopologicalManifoldHomset_with_category.element_class'> sage: Phi.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> M = Manifold(Integer(2), 'S^2', structure='topological') # the 2-dimensional sphere S^2 >>> U = M.open_subset('U') # complement of the North pole >>> c_xy = U.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# stereographic coordinates from the North pole >>> V = M.open_subset('V') # complement of the South pole >>> c_uv = V.chart(names=('u', 'v',)); (u, v,) = c_uv._first_ngens(2)# stereographic coordinates from the South pole >>> M.declare_union(U,V) # S^2 is the union of U and V >>> xy_to_uv = c_xy.transition_map(c_uv, (x/(x**Integer(2)+y**Integer(2)), y/(x**Integer(2)+y**Integer(2))), ... intersection_name='W', ... restrictions1=x**Integer(2)+y**Integer(2)!=Integer(0), ... restrictions2=u**Integer(2)+v**Integer(2)!=Integer(0)) >>> uv_to_xy = xy_to_uv.inverse() >>> N = Manifold(Integer(3), 'R^3', latex_name=r'\RR^3', structure='topological') # R^3 >>> c_cart = N.chart(names=('X', 'Y', 'Z',)); (X, Y, Z,) = c_cart._first_ngens(3)# Cartesian coordinates on R^3 >>> Phi = M.continuous_map(N, ... {(c_xy, c_cart): [Integer(2)*x/(Integer(1)+x**Integer(2)+y**Integer(2)), Integer(2)*y/(Integer(1)+x**Integer(2)+y**Integer(2)), (x**Integer(2)+y**Integer(2)-Integer(1))/(Integer(1)+x**Integer(2)+y**Integer(2))], ... (c_uv, c_cart): [Integer(2)*u/(Integer(1)+u**Integer(2)+v**Integer(2)), Integer(2)*v/(Integer(1)+u**Integer(2)+v**Integer(2)), (Integer(1)-u**Integer(2)-v**Integer(2))/(Integer(1)+u**Integer(2)+v**Integer(2))]}, ... name='Phi', latex_name=r'\Phi') >>> Phi Continuous map Phi from the 2-dimensional topological manifold S^2 to the 3-dimensional topological manifold R^3 >>> Phi.parent() Set of Morphisms from 2-dimensional topological manifold S^2 to 3-dimensional topological manifold R^3 in Category of manifolds over Real Field with 53 bits of precision >>> Phi.parent() is Hom(M, N) True >>> type(Phi) <class 'sage.manifolds.manifold_homset.TopologicalManifoldHomset_with_category.element_class'> >>> Phi.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - It is possible to create the map using - continuous_map()with only in a single pair of charts. The argument- coord_functionsis then a mere list of coordinate expressions (and not a dictionary) and the arguments- chart1and- chart2have to be provided if the charts differ from the default ones on the domain and/or codomain:- sage: Phi1 = M.continuous_map(N, [2*x/(1+x^2+y^2), 2*y/(1+x^2+y^2), (x^2+y^2-1)/(1+x^2+y^2)], ....: chart1=c_xy, chart2=c_cart, ....: name='Phi', latex_name=r'\Phi') - >>> from sage.all import * >>> Phi1 = M.continuous_map(N, [Integer(2)*x/(Integer(1)+x**Integer(2)+y**Integer(2)), Integer(2)*y/(Integer(1)+x**Integer(2)+y**Integer(2)), (x**Integer(2)+y**Integer(2)-Integer(1))/(Integer(1)+x**Integer(2)+y**Integer(2))], ... chart1=c_xy, chart2=c_cart, ... name='Phi', latex_name=r'\Phi') - Since - c_xyand- c_cartare the default charts on respectively- Mand- N, they can be omitted, so that the above declaration is equivalent to:- sage: Phi1 = M.continuous_map(N, [2*x/(1+x^2+y^2), 2*y/(1+x^2+y^2), (x^2+y^2-1)/(1+x^2+y^2)], ....: name='Phi', latex_name=r'\Phi') - >>> from sage.all import * >>> Phi1 = M.continuous_map(N, [Integer(2)*x/(Integer(1)+x**Integer(2)+y**Integer(2)), Integer(2)*y/(Integer(1)+x**Integer(2)+y**Integer(2)), (x**Integer(2)+y**Integer(2)-Integer(1))/(Integer(1)+x**Integer(2)+y**Integer(2))], ... name='Phi', latex_name=r'\Phi') - With such a declaration, the continuous map - Phi1is only partially defined on the manifold \(S^2\) as it is known in only one chart:- sage: Phi1.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - >>> from sage.all import * >>> Phi1.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - The definition can be completed by using - add_expr():- sage: Phi1.add_expr(c_uv, c_cart, [2*u/(1+u^2+v^2), 2*v/(1+u^2+v^2), (1-u^2-v^2)/(1+u^2+v^2)]) sage: Phi1.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> Phi1.add_expr(c_uv, c_cart, [Integer(2)*u/(Integer(1)+u**Integer(2)+v**Integer(2)), Integer(2)*v/(Integer(1)+u**Integer(2)+v**Integer(2)), (Integer(1)-u**Integer(2)-v**Integer(2))/(Integer(1)+u**Integer(2)+v**Integer(2))]) >>> Phi1.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - At this stage, - Phi1and- Phiare fully equivalent:- sage: Phi1 == Phi True - >>> from sage.all import * >>> Phi1 == Phi True - The map acts on points: - sage: np = M.point((0,0), chart=c_uv) # the North pole sage: Phi(np) Point on the 3-dimensional topological manifold R^3 sage: Phi(np).coord() # Cartesian coordinates (0, 0, 1) sage: sp = M.point((0,0), chart=c_xy) # the South pole sage: Phi(sp).coord() # Cartesian coordinates (0, 0, -1) - >>> from sage.all import * >>> np = M.point((Integer(0),Integer(0)), chart=c_uv) # the North pole >>> Phi(np) Point on the 3-dimensional topological manifold R^3 >>> Phi(np).coord() # Cartesian coordinates (0, 0, 1) >>> sp = M.point((Integer(0),Integer(0)), chart=c_xy) # the South pole >>> Phi(sp).coord() # Cartesian coordinates (0, 0, -1) - The test suite is passed: - sage: TestSuite(Phi).run() sage: TestSuite(Phi1).run() - >>> from sage.all import * >>> TestSuite(Phi).run() >>> TestSuite(Phi1).run() - Continuous maps can be composed by means of the operator - *. Let us introduce the map \(\RR^3 \to \RR^2\) corresponding to the projection from the point \((X, Y, Z) = (0, 0, 1)\) onto the equatorial plane \(Z = 0\):- sage: P = Manifold(2, 'R^2', latex_name=r'\RR^2', structure='topological') # R^2 (equatorial plane) sage: cP.<xP, yP> = P.chart() sage: Psi = N.continuous_map(P, (X/(1-Z), Y/(1-Z)), name='Psi', ....: latex_name=r'\Psi') sage: Psi Continuous map Psi from the 3-dimensional topological manifold R^3 to the 2-dimensional topological manifold R^2 sage: Psi.display() Psi: R^3 → R^2 (X, Y, Z) ↦ (xP, yP) = (-X/(Z - 1), -Y/(Z - 1)) - >>> from sage.all import * >>> P = Manifold(Integer(2), 'R^2', latex_name=r'\RR^2', structure='topological') # R^2 (equatorial plane) >>> cP = P.chart(names=('xP', 'yP',)); (xP, yP,) = cP._first_ngens(2) >>> Psi = N.continuous_map(P, (X/(Integer(1)-Z), Y/(Integer(1)-Z)), name='Psi', ... latex_name=r'\Psi') >>> Psi Continuous map Psi from the 3-dimensional topological manifold R^3 to the 2-dimensional topological manifold R^2 >>> Psi.display() Psi: R^3 → R^2 (X, Y, Z) ↦ (xP, yP) = (-X/(Z - 1), -Y/(Z - 1)) - Then we compose - Psiwith- Phi, thereby getting a map \(S^2 \to \RR^2\):- sage: ster = Psi * Phi ; ster Continuous map from the 2-dimensional topological manifold S^2 to the 2-dimensional topological manifold R^2 - >>> from sage.all import * >>> ster = Psi * Phi ; ster Continuous map from the 2-dimensional topological manifold S^2 to the 2-dimensional topological manifold R^2 - Let us test on the South pole ( - sp) that- steris indeed the composite of- Psiand- Phi:- sage: ster(sp) == Psi(Phi(sp)) True - >>> from sage.all import * >>> ster(sp) == Psi(Phi(sp)) True - Actually - steris the stereographic projection from the North pole, as its coordinate expression reveals:- sage: ster.display() S^2 → R^2 on U: (x, y) ↦ (xP, yP) = (x, y) on V: (u, v) ↦ (xP, yP) = (u/(u^2 + v^2), v/(u^2 + v^2)) - >>> from sage.all import * >>> ster.display() S^2 → R^2 on U: (x, y) ↦ (xP, yP) = (x, y) on V: (u, v) ↦ (xP, yP) = (u/(u^2 + v^2), v/(u^2 + v^2)) - If the codomain of a continuous map is 1-dimensional, the map can be defined by a single symbolic expression for each pair of charts and not by a list/tuple with a single element: - sage: N = Manifold(1, 'N', structure='topological') sage: c_N = N.chart('X') sage: Phi = M.continuous_map(N, {(c_xy, c_N): x^2+y^2, ....: (c_uv, c_N): 1/(u^2+v^2)}) sage: Psi = M.continuous_map(N, {(c_xy, c_N): [x^2+y^2], ....: (c_uv, c_N): [1/(u^2+v^2)]}) sage: Phi == Psi True - >>> from sage.all import * >>> N = Manifold(Integer(1), 'N', structure='topological') >>> c_N = N.chart('X') >>> Phi = M.continuous_map(N, {(c_xy, c_N): x**Integer(2)+y**Integer(2), ... (c_uv, c_N): Integer(1)/(u**Integer(2)+v**Integer(2))}) >>> Psi = M.continuous_map(N, {(c_xy, c_N): [x**Integer(2)+y**Integer(2)], ... (c_uv, c_N): [Integer(1)/(u**Integer(2)+v**Integer(2))]}) >>> Phi == Psi True - Next we construct an example of continuous map \(\RR \to \RR^2\): - sage: R = Manifold(1, 'R', structure='topological') # field R sage: T.<t> = R.chart() # canonical chart on R sage: R2 = Manifold(2, 'R^2', structure='topological') # R^2 sage: c_xy.<x,y> = R2.chart() # Cartesian coordinates on R^2 sage: Phi = R.continuous_map(R2, [cos(t), sin(t)], name='Phi'); Phi Continuous map Phi from the 1-dimensional topological manifold R to the 2-dimensional topological manifold R^2 sage: Phi.parent() Set of Morphisms from 1-dimensional topological manifold R to 2-dimensional topological manifold R^2 in Category of manifolds over Real Field with 53 bits of precision sage: Phi.parent() is Hom(R, R2) True sage: Phi.display() Phi: R → R^2 t ↦ (x, y) = (cos(t), sin(t)) - >>> from sage.all import * >>> R = Manifold(Integer(1), 'R', structure='topological') # field R >>> T = R.chart(names=('t',)); (t,) = T._first_ngens(1)# canonical chart on R >>> R2 = Manifold(Integer(2), 'R^2', structure='topological') # R^2 >>> c_xy = R2.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# Cartesian coordinates on R^2 >>> Phi = R.continuous_map(R2, [cos(t), sin(t)], name='Phi'); Phi Continuous map Phi from the 1-dimensional topological manifold R to the 2-dimensional topological manifold R^2 >>> Phi.parent() Set of Morphisms from 1-dimensional topological manifold R to 2-dimensional topological manifold R^2 in Category of manifolds over Real Field with 53 bits of precision >>> Phi.parent() is Hom(R, R2) True >>> Phi.display() Phi: R → R^2 t ↦ (x, y) = (cos(t), sin(t)) - An example of homeomorphism between the unit open disk and the Euclidean plane \(\RR^2\): - sage: D = R2.open_subset('D', coord_def={c_xy: x^2+y^2<1}) # the open unit disk sage: Phi = D.homeomorphism(R2, [x/sqrt(1-x^2-y^2), y/sqrt(1-x^2-y^2)], ....: name='Phi', latex_name=r'\Phi') sage: Phi Homeomorphism Phi from the Open subset D of the 2-dimensional topological manifold R^2 to the 2-dimensional topological manifold R^2 sage: Phi.parent() Set of Morphisms from Open subset D of the 2-dimensional topological manifold R^2 to 2-dimensional topological manifold R^2 in Category of manifolds over Real Field with 53 bits of precision sage: Phi.parent() is Hom(D, R2) True sage: Phi.display() Phi: D → R^2 (x, y) ↦ (x, y) = (x/sqrt(-x^2 - y^2 + 1), y/sqrt(-x^2 - y^2 + 1)) - >>> from sage.all import * >>> D = R2.open_subset('D', coord_def={c_xy: x**Integer(2)+y**Integer(2)<Integer(1)}) # the open unit disk >>> Phi = D.homeomorphism(R2, [x/sqrt(Integer(1)-x**Integer(2)-y**Integer(2)), y/sqrt(Integer(1)-x**Integer(2)-y**Integer(2))], ... name='Phi', latex_name=r'\Phi') >>> Phi Homeomorphism Phi from the Open subset D of the 2-dimensional topological manifold R^2 to the 2-dimensional topological manifold R^2 >>> Phi.parent() Set of Morphisms from Open subset D of the 2-dimensional topological manifold R^2 to 2-dimensional topological manifold R^2 in Category of manifolds over Real Field with 53 bits of precision >>> Phi.parent() is Hom(D, R2) True >>> Phi.display() Phi: D → R^2 (x, y) ↦ (x, y) = (x/sqrt(-x^2 - y^2 + 1), y/sqrt(-x^2 - y^2 + 1)) - The image of a point: - sage: p = D.point((1/2,0)) sage: q = Phi(p) ; q Point on the 2-dimensional topological manifold R^2 sage: q.coord() (1/3*sqrt(3), 0) - >>> from sage.all import * >>> p = D.point((Integer(1)/Integer(2),Integer(0))) >>> q = Phi(p) ; q Point on the 2-dimensional topological manifold R^2 >>> q.coord() (1/3*sqrt(3), 0) - The inverse homeomorphism is computed by - inverse():- sage: Phi.inverse() Homeomorphism Phi^(-1) from the 2-dimensional topological manifold R^2 to the Open subset D of the 2-dimensional topological manifold R^2 sage: Phi.inverse().display() Phi^(-1): R^2 → D (x, y) ↦ (x, y) = (x/sqrt(x^2 + y^2 + 1), y/sqrt(x^2 + y^2 + 1)) - >>> from sage.all import * >>> Phi.inverse() Homeomorphism Phi^(-1) from the 2-dimensional topological manifold R^2 to the Open subset D of the 2-dimensional topological manifold R^2 >>> Phi.inverse().display() Phi^(-1): R^2 → D (x, y) ↦ (x, y) = (x/sqrt(x^2 + y^2 + 1), y/sqrt(x^2 + y^2 + 1)) - Equivalently, one may use the notations - ^(-1)or- ~to get the inverse:- sage: Phi^(-1) is Phi.inverse() True sage: ~Phi is Phi.inverse() True - >>> from sage.all import * >>> Phi**(-Integer(1)) is Phi.inverse() True >>> ~Phi is Phi.inverse() True - Check that - ~Phiis indeed the inverse of- Phi:- sage: (~Phi)(q) == p True sage: Phi * ~Phi == R2.identity_map() True sage: ~Phi * Phi == D.identity_map() True - >>> from sage.all import * >>> (~Phi)(q) == p True >>> Phi * ~Phi == R2.identity_map() True >>> ~Phi * Phi == D.identity_map() True - The coordinate expression of the inverse homeomorphism: - sage: (~Phi).display() Phi^(-1): R^2 → D (x, y) ↦ (x, y) = (x/sqrt(x^2 + y^2 + 1), y/sqrt(x^2 + y^2 + 1)) - >>> from sage.all import * >>> (~Phi).display() Phi^(-1): R^2 → D (x, y) ↦ (x, y) = (x/sqrt(x^2 + y^2 + 1), y/sqrt(x^2 + y^2 + 1)) - A special case of homeomorphism: the identity map of the open unit disk: - sage: id = D.identity_map() ; id Identity map Id_D of the Open subset D of the 2-dimensional topological manifold R^2 sage: latex(id) \mathrm{Id}_{D} sage: id.parent() Set of Morphisms from Open subset D of the 2-dimensional topological manifold R^2 to Open subset D of the 2-dimensional topological manifold R^2 in Join of Category of subobjects of sets and Category of manifolds over Real Field with 53 bits of precision sage: id.parent() is Hom(D, D) True sage: id is Hom(D,D).one() # the identity element of the monoid Hom(D,D) True - >>> from sage.all import * >>> id = D.identity_map() ; id Identity map Id_D of the Open subset D of the 2-dimensional topological manifold R^2 >>> latex(id) \mathrm{Id}_{D} >>> id.parent() Set of Morphisms from Open subset D of the 2-dimensional topological manifold R^2 to Open subset D of the 2-dimensional topological manifold R^2 in Join of Category of subobjects of sets and Category of manifolds over Real Field with 53 bits of precision >>> id.parent() is Hom(D, D) True >>> id is Hom(D,D).one() # the identity element of the monoid Hom(D,D) True - The identity map acting on a point: - sage: id(p) Point on the 2-dimensional topological manifold R^2 sage: id(p) == p True sage: id(p) is p True - >>> from sage.all import * >>> id(p) Point on the 2-dimensional topological manifold R^2 >>> id(p) == p True >>> id(p) is p True - The coordinate expression of the identity map: - sage: id.display() Id_D: D → D (x, y) ↦ (x, y) - >>> from sage.all import * >>> id.display() Id_D: D → D (x, y) ↦ (x, y) - The identity map is its own inverse: - sage: id^(-1) is id True sage: ~id is id True - >>> from sage.all import * >>> id**(-Integer(1)) is id True >>> ~id is id True - add_expr(chart1, chart2, coord_functions)[source]¶
- Set a new coordinate representation of - self.- The previous expressions with respect to other charts are kept. To clear them, use - set_expr()instead.- INPUT: - chart1– chart for the coordinates on the map’s domain
- chart2– chart for the coordinates on the map’s codomain
- coord_functions– the coordinate symbolic expression of the map in the above charts: list (or tuple) of the coordinates of the image expressed in terms of the coordinates of the considered point; if the dimension of the arrival manifold is 1, a single coordinate expression can be passed instead of a tuple with a single element
 - Warning - If the map has already expressions in other charts, it is the user’s responsibility to make sure that the expression to be added is consistent with them. - EXAMPLES: - Polar representation of a planar rotation initially defined in Cartesian coordinates: - sage: M = Manifold(2, 'R^2', latex_name=r'\RR^2', structure='topological') # the Euclidean plane R^2 sage: c_xy.<x,y> = M.chart() # Cartesian coordinate on R^2 sage: U = M.open_subset('U', coord_def={c_xy: (y!=0, x<0)}) # the complement of the segment y=0 and x>0 sage: c_cart = c_xy.restrict(U) # Cartesian coordinates on U sage: c_spher.<r,ph> = U.chart(r'r:(0,+oo) ph:(0,2*pi):\phi') # spherical coordinates on U - >>> from sage.all import * >>> M = Manifold(Integer(2), 'R^2', latex_name=r'\RR^2', structure='topological') # the Euclidean plane R^2 >>> c_xy = M.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# Cartesian coordinate on R^2 >>> U = M.open_subset('U', coord_def={c_xy: (y!=Integer(0), x<Integer(0))}) # the complement of the segment y=0 and x>0 >>> c_cart = c_xy.restrict(U) # Cartesian coordinates on U >>> c_spher = U.chart(r'r:(0,+oo) ph:(0,2*pi):\phi', names=('r', 'ph',)); (r, ph,) = c_spher._first_ngens(2)# spherical coordinates on U - We construct the links between spherical coordinates and Cartesian ones: - sage: ch_cart_spher = c_cart.transition_map(c_spher, [sqrt(x*x+y*y), atan2(y,x)]) sage: ch_cart_spher.set_inverse(r*cos(ph), r*sin(ph)) Check of the inverse coordinate transformation: x == x *passed* y == y *passed* r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** NB: a failed report can reflect a mere lack of simplification. sage: rot = U.continuous_map(U, ((x - sqrt(3)*y)/2, (sqrt(3)*x + y)/2), ....: name='R') sage: rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - >>> from sage.all import * >>> ch_cart_spher = c_cart.transition_map(c_spher, [sqrt(x*x+y*y), atan2(y,x)]) >>> ch_cart_spher.set_inverse(r*cos(ph), r*sin(ph)) Check of the inverse coordinate transformation: x == x *passed* y == y *passed* r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** NB: a failed report can reflect a mere lack of simplification. >>> rot = U.continuous_map(U, ((x - sqrt(Integer(3))*y)/Integer(2), (sqrt(Integer(3))*x + y)/Integer(2)), ... name='R') >>> rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - If we calculate the expression in terms of spherical coordinates, via the method - display(), we notice some difficulties in- arctan2simplifications:- sage: rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, arctan2(1/2*(sqrt(3)*cos(ph) + sin(ph))*r, -1/2*(sqrt(3)*sin(ph) - cos(ph))*r)) - >>> from sage.all import * >>> rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, arctan2(1/2*(sqrt(3)*cos(ph) + sin(ph))*r, -1/2*(sqrt(3)*sin(ph) - cos(ph))*r)) - Therefore, we use the method - add_expr()to set the spherical-coordinate expression by hand:- sage: rot.add_expr(c_spher, c_spher, (r, ph+pi/3)) sage: rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, 1/3*pi + ph) - >>> from sage.all import * >>> rot.add_expr(c_spher, c_spher, (r, ph+pi/Integer(3))) >>> rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, 1/3*pi + ph) - The call to - add_expr()has not deleted the expression in terms of Cartesian coordinates, as we can check by printing the internal dictionary- _coord_expression, which stores the various internal representations of the continuous map:- sage: rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - If, on the contrary, we use - set_expr(), the expression in Cartesian coordinates is lost:- sage: rot.set_expr(c_spher, c_spher, (r, ph+pi/3)) sage: rot._coord_expression {(Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot.set_expr(c_spher, c_spher, (r, ph+pi/Integer(3))) >>> rot._coord_expression {(Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - It is recovered (thanks to the known change of coordinates) by a call to - display():- sage: rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) sage: rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) >>> rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - The rotation can be applied to a point by means of either coordinate system: - sage: p = M.point((1,2)) # p defined by its Cartesian coord. sage: q = rot(p) # q is computed by means of Cartesian coord. sage: p1 = M.point((sqrt(5), arctan(2)), chart=c_spher) # p1 is defined only in terms of c_spher sage: q1 = rot(p1) # computation by means of spherical coordinates sage: q1 == q True - >>> from sage.all import * >>> p = M.point((Integer(1),Integer(2))) # p defined by its Cartesian coord. >>> q = rot(p) # q is computed by means of Cartesian coord. >>> p1 = M.point((sqrt(Integer(5)), arctan(Integer(2))), chart=c_spher) # p1 is defined only in terms of c_spher >>> q1 = rot(p1) # computation by means of spherical coordinates >>> q1 == q True 
 - add_expression(chart1, chart2, coord_functions)[source]¶
- Set a new coordinate representation of - self.- The previous expressions with respect to other charts are kept. To clear them, use - set_expr()instead.- INPUT: - chart1– chart for the coordinates on the map’s domain
- chart2– chart for the coordinates on the map’s codomain
- coord_functions– the coordinate symbolic expression of the map in the above charts: list (or tuple) of the coordinates of the image expressed in terms of the coordinates of the considered point; if the dimension of the arrival manifold is 1, a single coordinate expression can be passed instead of a tuple with a single element
 - Warning - If the map has already expressions in other charts, it is the user’s responsibility to make sure that the expression to be added is consistent with them. - EXAMPLES: - Polar representation of a planar rotation initially defined in Cartesian coordinates: - sage: M = Manifold(2, 'R^2', latex_name=r'\RR^2', structure='topological') # the Euclidean plane R^2 sage: c_xy.<x,y> = M.chart() # Cartesian coordinate on R^2 sage: U = M.open_subset('U', coord_def={c_xy: (y!=0, x<0)}) # the complement of the segment y=0 and x>0 sage: c_cart = c_xy.restrict(U) # Cartesian coordinates on U sage: c_spher.<r,ph> = U.chart(r'r:(0,+oo) ph:(0,2*pi):\phi') # spherical coordinates on U - >>> from sage.all import * >>> M = Manifold(Integer(2), 'R^2', latex_name=r'\RR^2', structure='topological') # the Euclidean plane R^2 >>> c_xy = M.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# Cartesian coordinate on R^2 >>> U = M.open_subset('U', coord_def={c_xy: (y!=Integer(0), x<Integer(0))}) # the complement of the segment y=0 and x>0 >>> c_cart = c_xy.restrict(U) # Cartesian coordinates on U >>> c_spher = U.chart(r'r:(0,+oo) ph:(0,2*pi):\phi', names=('r', 'ph',)); (r, ph,) = c_spher._first_ngens(2)# spherical coordinates on U - We construct the links between spherical coordinates and Cartesian ones: - sage: ch_cart_spher = c_cart.transition_map(c_spher, [sqrt(x*x+y*y), atan2(y,x)]) sage: ch_cart_spher.set_inverse(r*cos(ph), r*sin(ph)) Check of the inverse coordinate transformation: x == x *passed* y == y *passed* r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** NB: a failed report can reflect a mere lack of simplification. sage: rot = U.continuous_map(U, ((x - sqrt(3)*y)/2, (sqrt(3)*x + y)/2), ....: name='R') sage: rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - >>> from sage.all import * >>> ch_cart_spher = c_cart.transition_map(c_spher, [sqrt(x*x+y*y), atan2(y,x)]) >>> ch_cart_spher.set_inverse(r*cos(ph), r*sin(ph)) Check of the inverse coordinate transformation: x == x *passed* y == y *passed* r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** NB: a failed report can reflect a mere lack of simplification. >>> rot = U.continuous_map(U, ((x - sqrt(Integer(3))*y)/Integer(2), (sqrt(Integer(3))*x + y)/Integer(2)), ... name='R') >>> rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - If we calculate the expression in terms of spherical coordinates, via the method - display(), we notice some difficulties in- arctan2simplifications:- sage: rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, arctan2(1/2*(sqrt(3)*cos(ph) + sin(ph))*r, -1/2*(sqrt(3)*sin(ph) - cos(ph))*r)) - >>> from sage.all import * >>> rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, arctan2(1/2*(sqrt(3)*cos(ph) + sin(ph))*r, -1/2*(sqrt(3)*sin(ph) - cos(ph))*r)) - Therefore, we use the method - add_expr()to set the spherical-coordinate expression by hand:- sage: rot.add_expr(c_spher, c_spher, (r, ph+pi/3)) sage: rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, 1/3*pi + ph) - >>> from sage.all import * >>> rot.add_expr(c_spher, c_spher, (r, ph+pi/Integer(3))) >>> rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, 1/3*pi + ph) - The call to - add_expr()has not deleted the expression in terms of Cartesian coordinates, as we can check by printing the internal dictionary- _coord_expression, which stores the various internal representations of the continuous map:- sage: rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - If, on the contrary, we use - set_expr(), the expression in Cartesian coordinates is lost:- sage: rot.set_expr(c_spher, c_spher, (r, ph+pi/3)) sage: rot._coord_expression {(Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot.set_expr(c_spher, c_spher, (r, ph+pi/Integer(3))) >>> rot._coord_expression {(Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - It is recovered (thanks to the known change of coordinates) by a call to - display():- sage: rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) sage: rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) >>> rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - The rotation can be applied to a point by means of either coordinate system: - sage: p = M.point((1,2)) # p defined by its Cartesian coord. sage: q = rot(p) # q is computed by means of Cartesian coord. sage: p1 = M.point((sqrt(5), arctan(2)), chart=c_spher) # p1 is defined only in terms of c_spher sage: q1 = rot(p1) # computation by means of spherical coordinates sage: q1 == q True - >>> from sage.all import * >>> p = M.point((Integer(1),Integer(2))) # p defined by its Cartesian coord. >>> q = rot(p) # q is computed by means of Cartesian coord. >>> p1 = M.point((sqrt(Integer(5)), arctan(Integer(2))), chart=c_spher) # p1 is defined only in terms of c_spher >>> q1 = rot(p1) # computation by means of spherical coordinates >>> q1 == q True 
 - coord_functions(chart1=None, chart2=None)[source]¶
- Return the functions of the coordinates representing - selfin a given pair of charts.- If these functions are not already known, they are computed from known ones by means of change-of-chart formulas. - INPUT: - chart1– (default:- None) chart on the domain of- self; if- None, the domain’s default chart is assumed
- chart2– (default:- None) chart on the codomain of- self; if- None, the codomain’s default chart is assumed
 - OUTPUT: - a - MultiCoordFunctionrepresenting the continuous map in the above two charts
 - EXAMPLES: - Continuous map from a 2-dimensional manifold to a 3-dimensional one: - sage: M = Manifold(2, 'M', structure='topological') sage: N = Manifold(3, 'N', structure='topological') sage: c_uv.<u,v> = M.chart() sage: c_xyz.<x,y,z> = N.chart() sage: Phi = M.continuous_map(N, (u*v, u/v, u+v), name='Phi', ....: latex_name=r'\Phi') sage: Phi.display() Phi: M → N (u, v) ↦ (x, y, z) = (u*v, u/v, u + v) sage: Phi.coord_functions(c_uv, c_xyz) Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) sage: Phi.coord_functions() # equivalent to above since 'uv' and 'xyz' are default charts Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) sage: type(Phi.coord_functions()) <class 'sage.manifolds.chart_func.MultiCoordFunction'> - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> N = Manifold(Integer(3), 'N', structure='topological') >>> c_uv = M.chart(names=('u', 'v',)); (u, v,) = c_uv._first_ngens(2) >>> c_xyz = N.chart(names=('x', 'y', 'z',)); (x, y, z,) = c_xyz._first_ngens(3) >>> Phi = M.continuous_map(N, (u*v, u/v, u+v), name='Phi', ... latex_name=r'\Phi') >>> Phi.display() Phi: M → N (u, v) ↦ (x, y, z) = (u*v, u/v, u + v) >>> Phi.coord_functions(c_uv, c_xyz) Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) >>> Phi.coord_functions() # equivalent to above since 'uv' and 'xyz' are default charts Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) >>> type(Phi.coord_functions()) <class 'sage.manifolds.chart_func.MultiCoordFunction'> - Coordinate representation in other charts: - sage: c_UV.<U,V> = M.chart() # new chart on M sage: ch_uv_UV = c_uv.transition_map(c_UV, [u-v, u+v]) sage: ch_uv_UV.inverse()(U,V) (1/2*U + 1/2*V, -1/2*U + 1/2*V) sage: c_XYZ.<X,Y,Z> = N.chart() # new chart on N sage: ch_xyz_XYZ = c_xyz.transition_map(c_XYZ, ....: [2*x-3*y+z, y+z-x, -x+2*y-z]) sage: ch_xyz_XYZ.inverse()(X,Y,Z) (3*X + Y + 4*Z, 2*X + Y + 3*Z, X + Y + Z) sage: Phi.coord_functions(c_UV, c_xyz) Coordinate functions (-1/4*U^2 + 1/4*V^2, -(U + V)/(U - V), V) on the Chart (M, (U, V)) sage: Phi.coord_functions(c_uv, c_XYZ) Coordinate functions (((2*u + 1)*v^2 + u*v - 3*u)/v, -((u - 1)*v^2 - u*v - u)/v, -((u + 1)*v^2 + u*v - 2*u)/v) on the Chart (M, (u, v)) sage: Phi.coord_functions(c_UV, c_XYZ) Coordinate functions (-1/2*(U^3 - (U - 2)*V^2 + V^3 - (U^2 + 2*U + 6)*V - 6*U)/(U - V), 1/4*(U^3 - (U + 4)*V^2 + V^3 - (U^2 - 4*U + 4)*V - 4*U)/(U - V), 1/4*(U^3 - (U - 4)*V^2 + V^3 - (U^2 + 4*U + 8)*V - 8*U)/(U - V)) on the Chart (M, (U, V)) - >>> from sage.all import * >>> c_UV = M.chart(names=('U', 'V',)); (U, V,) = c_UV._first_ngens(2)# new chart on M >>> ch_uv_UV = c_uv.transition_map(c_UV, [u-v, u+v]) >>> ch_uv_UV.inverse()(U,V) (1/2*U + 1/2*V, -1/2*U + 1/2*V) >>> c_XYZ = N.chart(names=('X', 'Y', 'Z',)); (X, Y, Z,) = c_XYZ._first_ngens(3)# new chart on N >>> ch_xyz_XYZ = c_xyz.transition_map(c_XYZ, ... [Integer(2)*x-Integer(3)*y+z, y+z-x, -x+Integer(2)*y-z]) >>> ch_xyz_XYZ.inverse()(X,Y,Z) (3*X + Y + 4*Z, 2*X + Y + 3*Z, X + Y + Z) >>> Phi.coord_functions(c_UV, c_xyz) Coordinate functions (-1/4*U^2 + 1/4*V^2, -(U + V)/(U - V), V) on the Chart (M, (U, V)) >>> Phi.coord_functions(c_uv, c_XYZ) Coordinate functions (((2*u + 1)*v^2 + u*v - 3*u)/v, -((u - 1)*v^2 - u*v - u)/v, -((u + 1)*v^2 + u*v - 2*u)/v) on the Chart (M, (u, v)) >>> Phi.coord_functions(c_UV, c_XYZ) Coordinate functions (-1/2*(U^3 - (U - 2)*V^2 + V^3 - (U^2 + 2*U + 6)*V - 6*U)/(U - V), 1/4*(U^3 - (U + 4)*V^2 + V^3 - (U^2 - 4*U + 4)*V - 4*U)/(U - V), 1/4*(U^3 - (U - 4)*V^2 + V^3 - (U^2 + 4*U + 8)*V - 8*U)/(U - V)) on the Chart (M, (U, V)) - Coordinate representation with respect to a subchart in the domain: - sage: A = M.open_subset('A', coord_def={c_uv: u>0}) sage: Phi.coord_functions(c_uv.restrict(A), c_xyz) Coordinate functions (u*v, u/v, u + v) on the Chart (A, (u, v)) - >>> from sage.all import * >>> A = M.open_subset('A', coord_def={c_uv: u>Integer(0)}) >>> Phi.coord_functions(c_uv.restrict(A), c_xyz) Coordinate functions (u*v, u/v, u + v) on the Chart (A, (u, v)) - Coordinate representation with respect to a superchart in the codomain: - sage: B = N.open_subset('B', coord_def={c_xyz: x<0}) sage: c_xyz_B = c_xyz.restrict(B) sage: Phi1 = M.continuous_map(B, {(c_uv, c_xyz_B): (u*v, u/v, u+v)}) sage: Phi1.coord_functions(c_uv, c_xyz_B) # definition charts Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) sage: Phi1.coord_functions(c_uv, c_xyz) # c_xyz = superchart of c_xyz_B Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) - >>> from sage.all import * >>> B = N.open_subset('B', coord_def={c_xyz: x<Integer(0)}) >>> c_xyz_B = c_xyz.restrict(B) >>> Phi1 = M.continuous_map(B, {(c_uv, c_xyz_B): (u*v, u/v, u+v)}) >>> Phi1.coord_functions(c_uv, c_xyz_B) # definition charts Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) >>> Phi1.coord_functions(c_uv, c_xyz) # c_xyz = superchart of c_xyz_B Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) - Coordinate representation with respect to a pair - (subchart, superchart):- sage: Phi1.coord_functions(c_uv.restrict(A), c_xyz) Coordinate functions (u*v, u/v, u + v) on the Chart (A, (u, v)) - >>> from sage.all import * >>> Phi1.coord_functions(c_uv.restrict(A), c_xyz) Coordinate functions (u*v, u/v, u + v) on the Chart (A, (u, v)) - Same example with SymPy as the symbolic calculus engine: - sage: M.set_calculus_method('sympy') sage: N.set_calculus_method('sympy') sage: Phi = M.continuous_map(N, (u*v, u/v, u+v), name='Phi', ....: latex_name=r'\Phi') sage: Phi.coord_functions(c_uv, c_xyz) Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) sage: Phi.coord_functions(c_UV, c_xyz) Coordinate functions (-U**2/4 + V**2/4, (-U - V)/(U - V), V) on the Chart (M, (U, V)) sage: Phi.coord_functions(c_UV, c_XYZ) Coordinate functions ((-U**3 + U**2*V + U*V**2 + 2*U*V + 6*U - V**3 - 2*V**2 + 6*V)/(2*(U - V)), (U**3/4 - U**2*V/4 - U*V**2/4 + U*V - U + V**3/4 - V**2 - V)/(U - V), (U**3 - U**2*V - U*V**2 - 4*U*V - 8*U + V**3 + 4*V**2 - 8*V)/(4*(U - V))) on the Chart (M, (U, V)) - >>> from sage.all import * >>> M.set_calculus_method('sympy') >>> N.set_calculus_method('sympy') >>> Phi = M.continuous_map(N, (u*v, u/v, u+v), name='Phi', ... latex_name=r'\Phi') >>> Phi.coord_functions(c_uv, c_xyz) Coordinate functions (u*v, u/v, u + v) on the Chart (M, (u, v)) >>> Phi.coord_functions(c_UV, c_xyz) Coordinate functions (-U**2/4 + V**2/4, (-U - V)/(U - V), V) on the Chart (M, (U, V)) >>> Phi.coord_functions(c_UV, c_XYZ) Coordinate functions ((-U**3 + U**2*V + U*V**2 + 2*U*V + 6*U - V**3 - 2*V**2 + 6*V)/(2*(U - V)), (U**3/4 - U**2*V/4 - U*V**2/4 + U*V - U + V**3/4 - V**2 - V)/(U - V), (U**3 - U**2*V - U*V**2 - 4*U*V - 8*U + V**3 + 4*V**2 - 8*V)/(4*(U - V))) on the Chart (M, (U, V)) 
 - disp(chart1=None, chart2=None)[source]¶
- Display the expression of - selfin one or more pair of charts.- If the expression is not known already, it is computed from some expression in other charts by means of change-of-coordinate formulas. - INPUT: - chart1– (default:- None) chart on the domain of- self; if- None, the display is performed on all the charts on the domain in which the map is known or computable via some change of coordinates
- chart2– (default:- None) chart on the codomain of- self; if- None, the display is performed on all the charts on the codomain in which the map is known or computable via some change of coordinates
 - The output is either text-formatted (console mode) or LaTeX-formatted (notebook mode). - EXAMPLES: - A simple reparametrization: - sage: R.<t> = manifolds.RealLine() sage: I = R.open_interval(0, 2*pi) sage: J = R.open_interval(2*pi, 6*pi) sage: h = J.continuous_map(I, ((t-2*pi)/2,), name='h') sage: h.display() h: (2*pi, 6*pi) → (0, 2*pi) t ↦ t = -pi + 1/2*t sage: latex(h.display()) \begin{array}{llcl} h:& \left(2 \, \pi, 6 \, \pi\right) & \longrightarrow & \left(0, 2 \, \pi\right) \\ & t & \longmapsto & t = -\pi + \frac{1}{2} \, t \end{array} - >>> from sage.all import * >>> R = manifolds.RealLine(names=('t',)); (t,) = R._first_ngens(1) >>> I = R.open_interval(Integer(0), Integer(2)*pi) >>> J = R.open_interval(Integer(2)*pi, Integer(6)*pi) >>> h = J.continuous_map(I, ((t-Integer(2)*pi)/Integer(2),), name='h') >>> h.display() h: (2*pi, 6*pi) → (0, 2*pi) t ↦ t = -pi + 1/2*t >>> latex(h.display()) \begin{array}{llcl} h:& \left(2 \, \pi, 6 \, \pi\right) & \longrightarrow & \left(0, 2 \, \pi\right) \\ & t & \longmapsto & t = -\pi + \frac{1}{2} \, t \end{array} - Standard embedding of the sphere \(S^2\) in \(\RR^3\): - sage: M = Manifold(2, 'S^2', structure='topological') # the 2-dimensional sphere S^2 sage: U = M.open_subset('U') # complement of the North pole sage: c_xy.<x,y> = U.chart() # stereographic coordinates from the North pole sage: V = M.open_subset('V') # complement of the South pole sage: c_uv.<u,v> = V.chart() # stereographic coordinates from the South pole sage: M.declare_union(U,V) # S^2 is the union of U and V sage: N = Manifold(3, 'R^3', latex_name=r'\RR^3', structure='topological') # R^3 sage: c_cart.<X,Y,Z> = N.chart() # Cartesian coordinates on R^3 sage: Phi = M.continuous_map(N, ....: {(c_xy, c_cart): [2*x/(1+x^2+y^2), 2*y/(1+x^2+y^2), (x^2+y^2-1)/(1+x^2+y^2)], ....: (c_uv, c_cart): [2*u/(1+u^2+v^2), 2*v/(1+u^2+v^2), (1-u^2-v^2)/(1+u^2+v^2)]}, ....: name='Phi', latex_name=r'\Phi') sage: Phi.display(c_xy, c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) sage: Phi.display(c_uv, c_cart) Phi: S^2 → R^3 on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> M = Manifold(Integer(2), 'S^2', structure='topological') # the 2-dimensional sphere S^2 >>> U = M.open_subset('U') # complement of the North pole >>> c_xy = U.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# stereographic coordinates from the North pole >>> V = M.open_subset('V') # complement of the South pole >>> c_uv = V.chart(names=('u', 'v',)); (u, v,) = c_uv._first_ngens(2)# stereographic coordinates from the South pole >>> M.declare_union(U,V) # S^2 is the union of U and V >>> N = Manifold(Integer(3), 'R^3', latex_name=r'\RR^3', structure='topological') # R^3 >>> c_cart = N.chart(names=('X', 'Y', 'Z',)); (X, Y, Z,) = c_cart._first_ngens(3)# Cartesian coordinates on R^3 >>> Phi = M.continuous_map(N, ... {(c_xy, c_cart): [Integer(2)*x/(Integer(1)+x**Integer(2)+y**Integer(2)), Integer(2)*y/(Integer(1)+x**Integer(2)+y**Integer(2)), (x**Integer(2)+y**Integer(2)-Integer(1))/(Integer(1)+x**Integer(2)+y**Integer(2))], ... (c_uv, c_cart): [Integer(2)*u/(Integer(1)+u**Integer(2)+v**Integer(2)), Integer(2)*v/(Integer(1)+u**Integer(2)+v**Integer(2)), (Integer(1)-u**Integer(2)-v**Integer(2))/(Integer(1)+u**Integer(2)+v**Integer(2))]}, ... name='Phi', latex_name=r'\Phi') >>> Phi.display(c_xy, c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) >>> Phi.display(c_uv, c_cart) Phi: S^2 → R^3 on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - The LaTeX output of that embedding is: - sage: latex(Phi.display(c_xy, c_cart)) \begin{array}{llcl} \Phi:& S^2 & \longrightarrow & \RR^3 \\ \text{on}\ U : & \left(x, y\right) & \longmapsto & \left(X, Y, Z\right) = \left(\frac{2 \, x}{x^{2} + y^{2} + 1}, \frac{2 \, y}{x^{2} + y^{2} + 1}, \frac{x^{2} + y^{2} - 1}{x^{2} + y^{2} + 1}\right) \end{array} - >>> from sage.all import * >>> latex(Phi.display(c_xy, c_cart)) \begin{array}{llcl} \Phi:& S^2 & \longrightarrow & \RR^3 \\ \text{on}\ U : & \left(x, y\right) & \longmapsto & \left(X, Y, Z\right) = \left(\frac{2 \, x}{x^{2} + y^{2} + 1}, \frac{2 \, y}{x^{2} + y^{2} + 1}, \frac{x^{2} + y^{2} - 1}{x^{2} + y^{2} + 1}\right) \end{array} - If the argument - chart2is not specified, the display is performed on all the charts on the codomain in which the map is known or computable via some change of coordinates (here only one chart:- c_cart):- sage: Phi.display(c_xy) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - >>> from sage.all import * >>> Phi.display(c_xy) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - Similarly, if the argument - chart1is omitted, the display is performed on all the charts on the domain of- Phiin which the map is known or computable via some change of coordinates:- sage: Phi.display(chart2=c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> Phi.display(chart2=c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - If neither - chart1nor- chart2is specified, the display is performed on all the pair of charts in which- Phiis known or computable via some change of coordinates:- sage: Phi.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> Phi.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - If a chart covers entirely the map’s domain, the mention “on …” is omitted: - sage: Phi.restrict(U).display() Phi: U → R^3 (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - >>> from sage.all import * >>> Phi.restrict(U).display() Phi: U → R^3 (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - A shortcut of - display()is- disp():- sage: Phi.disp() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> Phi.disp() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - Display when SymPy is the symbolic engine: - sage: M.set_calculus_method('sympy') sage: N.set_calculus_method('sympy') sage: Phi.display(c_xy, c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x**2 + y**2 + 1), 2*y/(x**2 + y**2 + 1), (x**2 + y**2 - 1)/(x**2 + y**2 + 1)) sage: latex(Phi.display(c_xy, c_cart)) \begin{array}{llcl} \Phi:& S^2 & \longrightarrow & \RR^3 \\ \text{on}\ U : & \left(x, y\right) & \longmapsto & \left(X, Y, Z\right) = \left(\frac{2 x}{x^{2} + y^{2} + 1}, \frac{2 y}{x^{2} + y^{2} + 1}, \frac{x^{2} + y^{2} - 1}{x^{2} + y^{2} + 1}\right) \end{array} - >>> from sage.all import * >>> M.set_calculus_method('sympy') >>> N.set_calculus_method('sympy') >>> Phi.display(c_xy, c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x**2 + y**2 + 1), 2*y/(x**2 + y**2 + 1), (x**2 + y**2 - 1)/(x**2 + y**2 + 1)) >>> latex(Phi.display(c_xy, c_cart)) \begin{array}{llcl} \Phi:& S^2 & \longrightarrow & \RR^3 \\ \text{on}\ U : & \left(x, y\right) & \longmapsto & \left(X, Y, Z\right) = \left(\frac{2 x}{x^{2} + y^{2} + 1}, \frac{2 y}{x^{2} + y^{2} + 1}, \frac{x^{2} + y^{2} - 1}{x^{2} + y^{2} + 1}\right) \end{array} 
 - display(chart1=None, chart2=None)[source]¶
- Display the expression of - selfin one or more pair of charts.- If the expression is not known already, it is computed from some expression in other charts by means of change-of-coordinate formulas. - INPUT: - chart1– (default:- None) chart on the domain of- self; if- None, the display is performed on all the charts on the domain in which the map is known or computable via some change of coordinates
- chart2– (default:- None) chart on the codomain of- self; if- None, the display is performed on all the charts on the codomain in which the map is known or computable via some change of coordinates
 - The output is either text-formatted (console mode) or LaTeX-formatted (notebook mode). - EXAMPLES: - A simple reparametrization: - sage: R.<t> = manifolds.RealLine() sage: I = R.open_interval(0, 2*pi) sage: J = R.open_interval(2*pi, 6*pi) sage: h = J.continuous_map(I, ((t-2*pi)/2,), name='h') sage: h.display() h: (2*pi, 6*pi) → (0, 2*pi) t ↦ t = -pi + 1/2*t sage: latex(h.display()) \begin{array}{llcl} h:& \left(2 \, \pi, 6 \, \pi\right) & \longrightarrow & \left(0, 2 \, \pi\right) \\ & t & \longmapsto & t = -\pi + \frac{1}{2} \, t \end{array} - >>> from sage.all import * >>> R = manifolds.RealLine(names=('t',)); (t,) = R._first_ngens(1) >>> I = R.open_interval(Integer(0), Integer(2)*pi) >>> J = R.open_interval(Integer(2)*pi, Integer(6)*pi) >>> h = J.continuous_map(I, ((t-Integer(2)*pi)/Integer(2),), name='h') >>> h.display() h: (2*pi, 6*pi) → (0, 2*pi) t ↦ t = -pi + 1/2*t >>> latex(h.display()) \begin{array}{llcl} h:& \left(2 \, \pi, 6 \, \pi\right) & \longrightarrow & \left(0, 2 \, \pi\right) \\ & t & \longmapsto & t = -\pi + \frac{1}{2} \, t \end{array} - Standard embedding of the sphere \(S^2\) in \(\RR^3\): - sage: M = Manifold(2, 'S^2', structure='topological') # the 2-dimensional sphere S^2 sage: U = M.open_subset('U') # complement of the North pole sage: c_xy.<x,y> = U.chart() # stereographic coordinates from the North pole sage: V = M.open_subset('V') # complement of the South pole sage: c_uv.<u,v> = V.chart() # stereographic coordinates from the South pole sage: M.declare_union(U,V) # S^2 is the union of U and V sage: N = Manifold(3, 'R^3', latex_name=r'\RR^3', structure='topological') # R^3 sage: c_cart.<X,Y,Z> = N.chart() # Cartesian coordinates on R^3 sage: Phi = M.continuous_map(N, ....: {(c_xy, c_cart): [2*x/(1+x^2+y^2), 2*y/(1+x^2+y^2), (x^2+y^2-1)/(1+x^2+y^2)], ....: (c_uv, c_cart): [2*u/(1+u^2+v^2), 2*v/(1+u^2+v^2), (1-u^2-v^2)/(1+u^2+v^2)]}, ....: name='Phi', latex_name=r'\Phi') sage: Phi.display(c_xy, c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) sage: Phi.display(c_uv, c_cart) Phi: S^2 → R^3 on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> M = Manifold(Integer(2), 'S^2', structure='topological') # the 2-dimensional sphere S^2 >>> U = M.open_subset('U') # complement of the North pole >>> c_xy = U.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# stereographic coordinates from the North pole >>> V = M.open_subset('V') # complement of the South pole >>> c_uv = V.chart(names=('u', 'v',)); (u, v,) = c_uv._first_ngens(2)# stereographic coordinates from the South pole >>> M.declare_union(U,V) # S^2 is the union of U and V >>> N = Manifold(Integer(3), 'R^3', latex_name=r'\RR^3', structure='topological') # R^3 >>> c_cart = N.chart(names=('X', 'Y', 'Z',)); (X, Y, Z,) = c_cart._first_ngens(3)# Cartesian coordinates on R^3 >>> Phi = M.continuous_map(N, ... {(c_xy, c_cart): [Integer(2)*x/(Integer(1)+x**Integer(2)+y**Integer(2)), Integer(2)*y/(Integer(1)+x**Integer(2)+y**Integer(2)), (x**Integer(2)+y**Integer(2)-Integer(1))/(Integer(1)+x**Integer(2)+y**Integer(2))], ... (c_uv, c_cart): [Integer(2)*u/(Integer(1)+u**Integer(2)+v**Integer(2)), Integer(2)*v/(Integer(1)+u**Integer(2)+v**Integer(2)), (Integer(1)-u**Integer(2)-v**Integer(2))/(Integer(1)+u**Integer(2)+v**Integer(2))]}, ... name='Phi', latex_name=r'\Phi') >>> Phi.display(c_xy, c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) >>> Phi.display(c_uv, c_cart) Phi: S^2 → R^3 on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - The LaTeX output of that embedding is: - sage: latex(Phi.display(c_xy, c_cart)) \begin{array}{llcl} \Phi:& S^2 & \longrightarrow & \RR^3 \\ \text{on}\ U : & \left(x, y\right) & \longmapsto & \left(X, Y, Z\right) = \left(\frac{2 \, x}{x^{2} + y^{2} + 1}, \frac{2 \, y}{x^{2} + y^{2} + 1}, \frac{x^{2} + y^{2} - 1}{x^{2} + y^{2} + 1}\right) \end{array} - >>> from sage.all import * >>> latex(Phi.display(c_xy, c_cart)) \begin{array}{llcl} \Phi:& S^2 & \longrightarrow & \RR^3 \\ \text{on}\ U : & \left(x, y\right) & \longmapsto & \left(X, Y, Z\right) = \left(\frac{2 \, x}{x^{2} + y^{2} + 1}, \frac{2 \, y}{x^{2} + y^{2} + 1}, \frac{x^{2} + y^{2} - 1}{x^{2} + y^{2} + 1}\right) \end{array} - If the argument - chart2is not specified, the display is performed on all the charts on the codomain in which the map is known or computable via some change of coordinates (here only one chart:- c_cart):- sage: Phi.display(c_xy) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - >>> from sage.all import * >>> Phi.display(c_xy) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - Similarly, if the argument - chart1is omitted, the display is performed on all the charts on the domain of- Phiin which the map is known or computable via some change of coordinates:- sage: Phi.display(chart2=c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> Phi.display(chart2=c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - If neither - chart1nor- chart2is specified, the display is performed on all the pair of charts in which- Phiis known or computable via some change of coordinates:- sage: Phi.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> Phi.display() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - If a chart covers entirely the map’s domain, the mention “on …” is omitted: - sage: Phi.restrict(U).display() Phi: U → R^3 (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - >>> from sage.all import * >>> Phi.restrict(U).display() Phi: U → R^3 (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) - A shortcut of - display()is- disp():- sage: Phi.disp() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - >>> from sage.all import * >>> Phi.disp() Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x^2 + y^2 + 1), 2*y/(x^2 + y^2 + 1), (x^2 + y^2 - 1)/(x^2 + y^2 + 1)) on V: (u, v) ↦ (X, Y, Z) = (2*u/(u^2 + v^2 + 1), 2*v/(u^2 + v^2 + 1), -(u^2 + v^2 - 1)/(u^2 + v^2 + 1)) - Display when SymPy is the symbolic engine: - sage: M.set_calculus_method('sympy') sage: N.set_calculus_method('sympy') sage: Phi.display(c_xy, c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x**2 + y**2 + 1), 2*y/(x**2 + y**2 + 1), (x**2 + y**2 - 1)/(x**2 + y**2 + 1)) sage: latex(Phi.display(c_xy, c_cart)) \begin{array}{llcl} \Phi:& S^2 & \longrightarrow & \RR^3 \\ \text{on}\ U : & \left(x, y\right) & \longmapsto & \left(X, Y, Z\right) = \left(\frac{2 x}{x^{2} + y^{2} + 1}, \frac{2 y}{x^{2} + y^{2} + 1}, \frac{x^{2} + y^{2} - 1}{x^{2} + y^{2} + 1}\right) \end{array} - >>> from sage.all import * >>> M.set_calculus_method('sympy') >>> N.set_calculus_method('sympy') >>> Phi.display(c_xy, c_cart) Phi: S^2 → R^3 on U: (x, y) ↦ (X, Y, Z) = (2*x/(x**2 + y**2 + 1), 2*y/(x**2 + y**2 + 1), (x**2 + y**2 - 1)/(x**2 + y**2 + 1)) >>> latex(Phi.display(c_xy, c_cart)) \begin{array}{llcl} \Phi:& S^2 & \longrightarrow & \RR^3 \\ \text{on}\ U : & \left(x, y\right) & \longmapsto & \left(X, Y, Z\right) = \left(\frac{2 x}{x^{2} + y^{2} + 1}, \frac{2 y}{x^{2} + y^{2} + 1}, \frac{x^{2} + y^{2} - 1}{x^{2} + y^{2} + 1}\right) \end{array} 
 - expr(chart1=None, chart2=None)[source]¶
- Return the expression of - selfin terms of specified coordinates.- If the expression is not already known, it is computed from some known expression by means of change-of-chart formulas. - INPUT: - chart1– (default:- None) chart on the map’s domain; if- None, the domain’s default chart is assumed
- chart2– (default:- None) chart on the map’s codomain; if- None, the codomain’s default chart is assumed
 - OUTPUT: - symbolic expression representing the continuous map in the above two charts 
 - EXAMPLES: - Continuous map from a 2-dimensional manifold to a 3-dimensional one: - sage: M = Manifold(2, 'M', structure='topological') sage: N = Manifold(3, 'N', structure='topological') sage: c_uv.<u,v> = M.chart() sage: c_xyz.<x,y,z> = N.chart() sage: Phi = M.continuous_map(N, (u*v, u/v, u+v), name='Phi', ....: latex_name=r'\Phi') sage: Phi.display() Phi: M → N (u, v) ↦ (x, y, z) = (u*v, u/v, u + v) sage: Phi.expr(c_uv, c_xyz) (u*v, u/v, u + v) sage: Phi.expr() # equivalent to above since 'uv' and 'xyz' are default charts (u*v, u/v, u + v) sage: type(Phi.expr()[0]) <class 'sage.symbolic.expression.Expression'> - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> N = Manifold(Integer(3), 'N', structure='topological') >>> c_uv = M.chart(names=('u', 'v',)); (u, v,) = c_uv._first_ngens(2) >>> c_xyz = N.chart(names=('x', 'y', 'z',)); (x, y, z,) = c_xyz._first_ngens(3) >>> Phi = M.continuous_map(N, (u*v, u/v, u+v), name='Phi', ... latex_name=r'\Phi') >>> Phi.display() Phi: M → N (u, v) ↦ (x, y, z) = (u*v, u/v, u + v) >>> Phi.expr(c_uv, c_xyz) (u*v, u/v, u + v) >>> Phi.expr() # equivalent to above since 'uv' and 'xyz' are default charts (u*v, u/v, u + v) >>> type(Phi.expr()[Integer(0)]) <class 'sage.symbolic.expression.Expression'> - Expressions in other charts: - sage: c_UV.<U,V> = M.chart() # new chart on M sage: ch_uv_UV = c_uv.transition_map(c_UV, [u-v, u+v]) sage: ch_uv_UV.inverse()(U,V) (1/2*U + 1/2*V, -1/2*U + 1/2*V) sage: c_XYZ.<X,Y,Z> = N.chart() # new chart on N sage: ch_xyz_XYZ = c_xyz.transition_map(c_XYZ, ....: [2*x-3*y+z, y+z-x, -x+2*y-z]) sage: ch_xyz_XYZ.inverse()(X,Y,Z) (3*X + Y + 4*Z, 2*X + Y + 3*Z, X + Y + Z) sage: Phi.expr(c_UV, c_xyz) (-1/4*U^2 + 1/4*V^2, -(U + V)/(U - V), V) sage: Phi.expr(c_uv, c_XYZ) (((2*u + 1)*v^2 + u*v - 3*u)/v, -((u - 1)*v^2 - u*v - u)/v, -((u + 1)*v^2 + u*v - 2*u)/v) sage: Phi.expr(c_UV, c_XYZ) (-1/2*(U^3 - (U - 2)*V^2 + V^3 - (U^2 + 2*U + 6)*V - 6*U)/(U - V), 1/4*(U^3 - (U + 4)*V^2 + V^3 - (U^2 - 4*U + 4)*V - 4*U)/(U - V), 1/4*(U^3 - (U - 4)*V^2 + V^3 - (U^2 + 4*U + 8)*V - 8*U)/(U - V)) - >>> from sage.all import * >>> c_UV = M.chart(names=('U', 'V',)); (U, V,) = c_UV._first_ngens(2)# new chart on M >>> ch_uv_UV = c_uv.transition_map(c_UV, [u-v, u+v]) >>> ch_uv_UV.inverse()(U,V) (1/2*U + 1/2*V, -1/2*U + 1/2*V) >>> c_XYZ = N.chart(names=('X', 'Y', 'Z',)); (X, Y, Z,) = c_XYZ._first_ngens(3)# new chart on N >>> ch_xyz_XYZ = c_xyz.transition_map(c_XYZ, ... [Integer(2)*x-Integer(3)*y+z, y+z-x, -x+Integer(2)*y-z]) >>> ch_xyz_XYZ.inverse()(X,Y,Z) (3*X + Y + 4*Z, 2*X + Y + 3*Z, X + Y + Z) >>> Phi.expr(c_UV, c_xyz) (-1/4*U^2 + 1/4*V^2, -(U + V)/(U - V), V) >>> Phi.expr(c_uv, c_XYZ) (((2*u + 1)*v^2 + u*v - 3*u)/v, -((u - 1)*v^2 - u*v - u)/v, -((u + 1)*v^2 + u*v - 2*u)/v) >>> Phi.expr(c_UV, c_XYZ) (-1/2*(U^3 - (U - 2)*V^2 + V^3 - (U^2 + 2*U + 6)*V - 6*U)/(U - V), 1/4*(U^3 - (U + 4)*V^2 + V^3 - (U^2 - 4*U + 4)*V - 4*U)/(U - V), 1/4*(U^3 - (U - 4)*V^2 + V^3 - (U^2 + 4*U + 8)*V - 8*U)/(U - V)) - A rotation in some Euclidean plane: - sage: M = Manifold(2, 'M', structure='topological') # the plane (minus a segment to have global regular spherical coordinates) sage: c_spher.<r,ph> = M.chart(r'r:(0,+oo) ph:(0,2*pi):\phi') # spherical coordinates on the plane sage: rot = M.continuous_map(M, (r, ph+pi/3), name='R') # pi/3 rotation around r=0 sage: rot.expr() (r, 1/3*pi + ph) - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') # the plane (minus a segment to have global regular spherical coordinates) >>> c_spher = M.chart(r'r:(0,+oo) ph:(0,2*pi):\phi', names=('r', 'ph',)); (r, ph,) = c_spher._first_ngens(2)# spherical coordinates on the plane >>> rot = M.continuous_map(M, (r, ph+pi/Integer(3)), name='R') # pi/3 rotation around r=0 >>> rot.expr() (r, 1/3*pi + ph) - Expression of the rotation in terms of Cartesian coordinates: - sage: c_cart.<x,y> = M.chart() # Declaration of Cartesian coordinates sage: ch_spher_cart = c_spher.transition_map(c_cart, ....: [r*cos(ph), r*sin(ph)]) # relation to spherical coordinates sage: ch_spher_cart.set_inverse(sqrt(x^2+y^2), atan2(y,x)) Check of the inverse coordinate transformation: r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** x == x *passed* y == y *passed* NB: a failed report can reflect a mere lack of simplification. sage: rot.expr(c_cart, c_cart) (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - >>> from sage.all import * >>> c_cart = M.chart(names=('x', 'y',)); (x, y,) = c_cart._first_ngens(2)# Declaration of Cartesian coordinates >>> ch_spher_cart = c_spher.transition_map(c_cart, ... [r*cos(ph), r*sin(ph)]) # relation to spherical coordinates >>> ch_spher_cart.set_inverse(sqrt(x**Integer(2)+y**Integer(2)), atan2(y,x)) Check of the inverse coordinate transformation: r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** x == x *passed* y == y *passed* NB: a failed report can reflect a mere lack of simplification. >>> rot.expr(c_cart, c_cart) (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) 
 - expression(chart1=None, chart2=None)[source]¶
- Return the expression of - selfin terms of specified coordinates.- If the expression is not already known, it is computed from some known expression by means of change-of-chart formulas. - INPUT: - chart1– (default:- None) chart on the map’s domain; if- None, the domain’s default chart is assumed
- chart2– (default:- None) chart on the map’s codomain; if- None, the codomain’s default chart is assumed
 - OUTPUT: - symbolic expression representing the continuous map in the above two charts 
 - EXAMPLES: - Continuous map from a 2-dimensional manifold to a 3-dimensional one: - sage: M = Manifold(2, 'M', structure='topological') sage: N = Manifold(3, 'N', structure='topological') sage: c_uv.<u,v> = M.chart() sage: c_xyz.<x,y,z> = N.chart() sage: Phi = M.continuous_map(N, (u*v, u/v, u+v), name='Phi', ....: latex_name=r'\Phi') sage: Phi.display() Phi: M → N (u, v) ↦ (x, y, z) = (u*v, u/v, u + v) sage: Phi.expr(c_uv, c_xyz) (u*v, u/v, u + v) sage: Phi.expr() # equivalent to above since 'uv' and 'xyz' are default charts (u*v, u/v, u + v) sage: type(Phi.expr()[0]) <class 'sage.symbolic.expression.Expression'> - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> N = Manifold(Integer(3), 'N', structure='topological') >>> c_uv = M.chart(names=('u', 'v',)); (u, v,) = c_uv._first_ngens(2) >>> c_xyz = N.chart(names=('x', 'y', 'z',)); (x, y, z,) = c_xyz._first_ngens(3) >>> Phi = M.continuous_map(N, (u*v, u/v, u+v), name='Phi', ... latex_name=r'\Phi') >>> Phi.display() Phi: M → N (u, v) ↦ (x, y, z) = (u*v, u/v, u + v) >>> Phi.expr(c_uv, c_xyz) (u*v, u/v, u + v) >>> Phi.expr() # equivalent to above since 'uv' and 'xyz' are default charts (u*v, u/v, u + v) >>> type(Phi.expr()[Integer(0)]) <class 'sage.symbolic.expression.Expression'> - Expressions in other charts: - sage: c_UV.<U,V> = M.chart() # new chart on M sage: ch_uv_UV = c_uv.transition_map(c_UV, [u-v, u+v]) sage: ch_uv_UV.inverse()(U,V) (1/2*U + 1/2*V, -1/2*U + 1/2*V) sage: c_XYZ.<X,Y,Z> = N.chart() # new chart on N sage: ch_xyz_XYZ = c_xyz.transition_map(c_XYZ, ....: [2*x-3*y+z, y+z-x, -x+2*y-z]) sage: ch_xyz_XYZ.inverse()(X,Y,Z) (3*X + Y + 4*Z, 2*X + Y + 3*Z, X + Y + Z) sage: Phi.expr(c_UV, c_xyz) (-1/4*U^2 + 1/4*V^2, -(U + V)/(U - V), V) sage: Phi.expr(c_uv, c_XYZ) (((2*u + 1)*v^2 + u*v - 3*u)/v, -((u - 1)*v^2 - u*v - u)/v, -((u + 1)*v^2 + u*v - 2*u)/v) sage: Phi.expr(c_UV, c_XYZ) (-1/2*(U^3 - (U - 2)*V^2 + V^3 - (U^2 + 2*U + 6)*V - 6*U)/(U - V), 1/4*(U^3 - (U + 4)*V^2 + V^3 - (U^2 - 4*U + 4)*V - 4*U)/(U - V), 1/4*(U^3 - (U - 4)*V^2 + V^3 - (U^2 + 4*U + 8)*V - 8*U)/(U - V)) - >>> from sage.all import * >>> c_UV = M.chart(names=('U', 'V',)); (U, V,) = c_UV._first_ngens(2)# new chart on M >>> ch_uv_UV = c_uv.transition_map(c_UV, [u-v, u+v]) >>> ch_uv_UV.inverse()(U,V) (1/2*U + 1/2*V, -1/2*U + 1/2*V) >>> c_XYZ = N.chart(names=('X', 'Y', 'Z',)); (X, Y, Z,) = c_XYZ._first_ngens(3)# new chart on N >>> ch_xyz_XYZ = c_xyz.transition_map(c_XYZ, ... [Integer(2)*x-Integer(3)*y+z, y+z-x, -x+Integer(2)*y-z]) >>> ch_xyz_XYZ.inverse()(X,Y,Z) (3*X + Y + 4*Z, 2*X + Y + 3*Z, X + Y + Z) >>> Phi.expr(c_UV, c_xyz) (-1/4*U^2 + 1/4*V^2, -(U + V)/(U - V), V) >>> Phi.expr(c_uv, c_XYZ) (((2*u + 1)*v^2 + u*v - 3*u)/v, -((u - 1)*v^2 - u*v - u)/v, -((u + 1)*v^2 + u*v - 2*u)/v) >>> Phi.expr(c_UV, c_XYZ) (-1/2*(U^3 - (U - 2)*V^2 + V^3 - (U^2 + 2*U + 6)*V - 6*U)/(U - V), 1/4*(U^3 - (U + 4)*V^2 + V^3 - (U^2 - 4*U + 4)*V - 4*U)/(U - V), 1/4*(U^3 - (U - 4)*V^2 + V^3 - (U^2 + 4*U + 8)*V - 8*U)/(U - V)) - A rotation in some Euclidean plane: - sage: M = Manifold(2, 'M', structure='topological') # the plane (minus a segment to have global regular spherical coordinates) sage: c_spher.<r,ph> = M.chart(r'r:(0,+oo) ph:(0,2*pi):\phi') # spherical coordinates on the plane sage: rot = M.continuous_map(M, (r, ph+pi/3), name='R') # pi/3 rotation around r=0 sage: rot.expr() (r, 1/3*pi + ph) - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') # the plane (minus a segment to have global regular spherical coordinates) >>> c_spher = M.chart(r'r:(0,+oo) ph:(0,2*pi):\phi', names=('r', 'ph',)); (r, ph,) = c_spher._first_ngens(2)# spherical coordinates on the plane >>> rot = M.continuous_map(M, (r, ph+pi/Integer(3)), name='R') # pi/3 rotation around r=0 >>> rot.expr() (r, 1/3*pi + ph) - Expression of the rotation in terms of Cartesian coordinates: - sage: c_cart.<x,y> = M.chart() # Declaration of Cartesian coordinates sage: ch_spher_cart = c_spher.transition_map(c_cart, ....: [r*cos(ph), r*sin(ph)]) # relation to spherical coordinates sage: ch_spher_cart.set_inverse(sqrt(x^2+y^2), atan2(y,x)) Check of the inverse coordinate transformation: r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** x == x *passed* y == y *passed* NB: a failed report can reflect a mere lack of simplification. sage: rot.expr(c_cart, c_cart) (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - >>> from sage.all import * >>> c_cart = M.chart(names=('x', 'y',)); (x, y,) = c_cart._first_ngens(2)# Declaration of Cartesian coordinates >>> ch_spher_cart = c_spher.transition_map(c_cart, ... [r*cos(ph), r*sin(ph)]) # relation to spherical coordinates >>> ch_spher_cart.set_inverse(sqrt(x**Integer(2)+y**Integer(2)), atan2(y,x)) Check of the inverse coordinate transformation: r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** x == x *passed* y == y *passed* NB: a failed report can reflect a mere lack of simplification. >>> rot.expr(c_cart, c_cart) (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) 
 - image(subset=None, inverse=None)[source]¶
- Return the image of - selfor the image of- subsetunder- self.- INPUT: - inverse– (default:- None) continuous map from- map.codomain()to- map.domain(), which once restricted to the image of \(\Phi\) is the inverse of \(\Phi\) onto its image if the latter exists (NB: no check of this is performed)
- subset– (default: the domain of- map) a subset of the domain of- self
 - EXAMPLES: - sage: M = Manifold(2, 'M', structure='topological') sage: N = Manifold(1, 'N', ambient=M, structure='topological') sage: CM.<x,y> = M.chart() sage: CN.<u> = N.chart(coord_restrictions=lambda u: [u > -1, u < 1]) sage: Phi = N.continuous_map(M, {(CN,CM): [u, u^2]}, name='Phi') sage: Phi.image() Image of the Continuous map Phi from the 1-dimensional topological submanifold N immersed in the 2-dimensional topological manifold M to the 2-dimensional topological manifold M sage: S = N.subset('S') sage: Phi_S = Phi.image(S); Phi_S Image of the Subset S of the 1-dimensional topological submanifold N immersed in the 2-dimensional topological manifold M under the Continuous map Phi from the 1-dimensional topological submanifold N immersed in the 2-dimensional topological manifold M to the 2-dimensional topological manifold M sage: Phi_S.is_subset(M) True - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> N = Manifold(Integer(1), 'N', ambient=M, structure='topological') >>> CM = M.chart(names=('x', 'y',)); (x, y,) = CM._first_ngens(2) >>> CN = N.chart(coord_restrictions=lambda u: [u > -Integer(1), u < Integer(1)], names=('u',)); (u,) = CN._first_ngens(1) >>> Phi = N.continuous_map(M, {(CN,CM): [u, u**Integer(2)]}, name='Phi') >>> Phi.image() Image of the Continuous map Phi from the 1-dimensional topological submanifold N immersed in the 2-dimensional topological manifold M to the 2-dimensional topological manifold M >>> S = N.subset('S') >>> Phi_S = Phi.image(S); Phi_S Image of the Subset S of the 1-dimensional topological submanifold N immersed in the 2-dimensional topological manifold M under the Continuous map Phi from the 1-dimensional topological submanifold N immersed in the 2-dimensional topological manifold M to the 2-dimensional topological manifold M >>> Phi_S.is_subset(M) True 
 - inverse()[source]¶
- Return the inverse of - selfif it is an isomorphism.- OUTPUT: the inverse isomorphism - EXAMPLES: - The inverse of a rotation in the Euclidean plane: - sage: M = Manifold(2, 'R^2', latex_name=r'\RR^2', structure='topological') sage: c_cart.<x,y> = M.chart() - >>> from sage.all import * >>> M = Manifold(Integer(2), 'R^2', latex_name=r'\RR^2', structure='topological') >>> c_cart = M.chart(names=('x', 'y',)); (x, y,) = c_cart._first_ngens(2) - A pi/3 rotation around the origin: - sage: rot = M.homeomorphism(M, ((x - sqrt(3)*y)/2, (sqrt(3)*x + y)/2), ....: name='R') sage: rot.inverse() Homeomorphism R^(-1) of the 2-dimensional topological manifold R^2 sage: rot.inverse().display() R^(-1): R^2 → R^2 (x, y) ↦ (1/2*sqrt(3)*y + 1/2*x, -1/2*sqrt(3)*x + 1/2*y) - >>> from sage.all import * >>> rot = M.homeomorphism(M, ((x - sqrt(Integer(3))*y)/Integer(2), (sqrt(Integer(3))*x + y)/Integer(2)), ... name='R') >>> rot.inverse() Homeomorphism R^(-1) of the 2-dimensional topological manifold R^2 >>> rot.inverse().display() R^(-1): R^2 → R^2 (x, y) ↦ (1/2*sqrt(3)*y + 1/2*x, -1/2*sqrt(3)*x + 1/2*y) - Checking that applying successively the homeomorphism and its inverse results in the identity: - sage: (a, b) = var('a b') sage: p = M.point((a,b)) # a generic point on M sage: q = rot(p) sage: p1 = rot.inverse()(q) sage: p1 == p True - >>> from sage.all import * >>> (a, b) = var('a b') >>> p = M.point((a,b)) # a generic point on M >>> q = rot(p) >>> p1 = rot.inverse()(q) >>> p1 == p True - The result is cached: - sage: rot.inverse() is rot.inverse() True - >>> from sage.all import * >>> rot.inverse() is rot.inverse() True - The notations - ^(-1)or- ~can also be used for the inverse:- sage: rot^(-1) is rot.inverse() True sage: ~rot is rot.inverse() True - >>> from sage.all import * >>> rot**(-Integer(1)) is rot.inverse() True >>> ~rot is rot.inverse() True - An example with multiple charts: the equatorial symmetry on the 2-sphere: - sage: M = Manifold(2, 'M', structure='topological') # the 2-dimensional sphere S^2 sage: U = M.open_subset('U') # complement of the North pole sage: c_xy.<x,y> = U.chart() # stereographic coordinates from the North pole sage: V = M.open_subset('V') # complement of the South pole sage: c_uv.<u,v> = V.chart() # stereographic coordinates from the South pole sage: M.declare_union(U,V) # S^2 is the union of U and V sage: xy_to_uv = c_xy.transition_map(c_uv, (x/(x^2+y^2), y/(x^2+y^2)), ....: intersection_name='W', ....: restrictions1=x^2+y^2!=0, ....: restrictions2=u^2+v^2!=0) sage: uv_to_xy = xy_to_uv.inverse() sage: s = M.homeomorphism(M, {(c_xy, c_uv): [x, y], (c_uv, c_xy): [u, v]}, ....: name='s') sage: s.display() s: M → M on U: (x, y) ↦ (u, v) = (x, y) on V: (u, v) ↦ (x, y) = (u, v) sage: si = s.inverse(); si Homeomorphism s^(-1) of the 2-dimensional topological manifold M sage: si.display() s^(-1): M → M on U: (x, y) ↦ (u, v) = (x, y) on V: (u, v) ↦ (x, y) = (u, v) - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') # the 2-dimensional sphere S^2 >>> U = M.open_subset('U') # complement of the North pole >>> c_xy = U.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# stereographic coordinates from the North pole >>> V = M.open_subset('V') # complement of the South pole >>> c_uv = V.chart(names=('u', 'v',)); (u, v,) = c_uv._first_ngens(2)# stereographic coordinates from the South pole >>> M.declare_union(U,V) # S^2 is the union of U and V >>> xy_to_uv = c_xy.transition_map(c_uv, (x/(x**Integer(2)+y**Integer(2)), y/(x**Integer(2)+y**Integer(2))), ... intersection_name='W', ... restrictions1=x**Integer(2)+y**Integer(2)!=Integer(0), ... restrictions2=u**Integer(2)+v**Integer(2)!=Integer(0)) >>> uv_to_xy = xy_to_uv.inverse() >>> s = M.homeomorphism(M, {(c_xy, c_uv): [x, y], (c_uv, c_xy): [u, v]}, ... name='s') >>> s.display() s: M → M on U: (x, y) ↦ (u, v) = (x, y) on V: (u, v) ↦ (x, y) = (u, v) >>> si = s.inverse(); si Homeomorphism s^(-1) of the 2-dimensional topological manifold M >>> si.display() s^(-1): M → M on U: (x, y) ↦ (u, v) = (x, y) on V: (u, v) ↦ (x, y) = (u, v) - The equatorial symmetry is of course an involution: - sage: si == s True - >>> from sage.all import * >>> si == s True 
 - is_identity()[source]¶
- Check whether - selfis an identity map.- EXAMPLES: - Tests on continuous maps of a 2-dimensional manifold: - sage: M = Manifold(2, 'M', structure='topological') sage: X.<x,y> = M.chart() sage: M.identity_map().is_identity() # obviously... True sage: Hom(M, M).one().is_identity() # a variant of the obvious True sage: a = M.continuous_map(M, coord_functions={(X,X): (x, y)}) sage: a.is_identity() True sage: a = M.continuous_map(M, coord_functions={(X,X): (x, y+1)}) sage: a.is_identity() False - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> X = M.chart(names=('x', 'y',)); (x, y,) = X._first_ngens(2) >>> M.identity_map().is_identity() # obviously... True >>> Hom(M, M).one().is_identity() # a variant of the obvious True >>> a = M.continuous_map(M, coord_functions={(X,X): (x, y)}) >>> a.is_identity() True >>> a = M.continuous_map(M, coord_functions={(X,X): (x, y+Integer(1))}) >>> a.is_identity() False - Of course, if the codomain of the map does not coincide with its domain, the outcome is - False:- sage: N = Manifold(2, 'N', structure='topological') sage: Y.<u,v> = N.chart() sage: a = M.continuous_map(N, {(X,Y): (x, y)}) sage: a.display() M → N (x, y) ↦ (u, v) = (x, y) sage: a.is_identity() False - >>> from sage.all import * >>> N = Manifold(Integer(2), 'N', structure='topological') >>> Y = N.chart(names=('u', 'v',)); (u, v,) = Y._first_ngens(2) >>> a = M.continuous_map(N, {(X,Y): (x, y)}) >>> a.display() M → N (x, y) ↦ (u, v) = (x, y) >>> a.is_identity() False 
 - preimage(codomain_subset, name=None, latex_name=None)[source]¶
- Return the preimage of - codomain_subsetunder- self.- An alias is - pullback().- INPUT: - codomain_subset– an instance of- ManifoldSubset
- name– string; name (symbol) given to the subset
- latex_name– string (default:- None); LaTeX symbol to denote the subset; if none are provided, it is set to- name
 - OUTPUT: - either a - TopologicalManifoldor a- ManifoldSubsetPullback
 - EXAMPLES: - sage: R = Manifold(1, 'R', structure='topological') # field R sage: T.<t> = R.chart() # canonical chart on R sage: R2 = Manifold(2, 'R^2', structure='topological') # R^2 sage: c_xy.<x,y> = R2.chart() # Cartesian coordinates on R^2 sage: Phi = R.continuous_map(R2, [cos(t), sin(t)], name='Phi'); Phi Continuous map Phi from the 1-dimensional topological manifold R to the 2-dimensional topological manifold R^2 sage: Q1 = R2.open_subset('Q1', coord_def={c_xy: [x>0, y>0]}); Q1 Open subset Q1 of the 2-dimensional topological manifold R^2 sage: Phi_inv_Q1 = Phi.preimage(Q1); Phi_inv_Q1 Subset Phi_inv_Q1 of the 1-dimensional topological manifold R sage: R.point([pi/4]) in Phi_inv_Q1 True sage: R.point([0]) in Phi_inv_Q1 False sage: R.point([3*pi/4]) in Phi_inv_Q1 False - >>> from sage.all import * >>> R = Manifold(Integer(1), 'R', structure='topological') # field R >>> T = R.chart(names=('t',)); (t,) = T._first_ngens(1)# canonical chart on R >>> R2 = Manifold(Integer(2), 'R^2', structure='topological') # R^2 >>> c_xy = R2.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# Cartesian coordinates on R^2 >>> Phi = R.continuous_map(R2, [cos(t), sin(t)], name='Phi'); Phi Continuous map Phi from the 1-dimensional topological manifold R to the 2-dimensional topological manifold R^2 >>> Q1 = R2.open_subset('Q1', coord_def={c_xy: [x>Integer(0), y>Integer(0)]}); Q1 Open subset Q1 of the 2-dimensional topological manifold R^2 >>> Phi_inv_Q1 = Phi.preimage(Q1); Phi_inv_Q1 Subset Phi_inv_Q1 of the 1-dimensional topological manifold R >>> R.point([pi/Integer(4)]) in Phi_inv_Q1 True >>> R.point([Integer(0)]) in Phi_inv_Q1 False >>> R.point([Integer(3)*pi/Integer(4)]) in Phi_inv_Q1 False - The identity map is handled specially: - sage: M = Manifold(2, 'M', structure='topological') sage: X.<x,y> = M.chart() sage: M.identity_map().preimage(M) 2-dimensional topological manifold M sage: M.identity_map().preimage(M) is M True - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> X = M.chart(names=('x', 'y',)); (x, y,) = X._first_ngens(2) >>> M.identity_map().preimage(M) 2-dimensional topological manifold M >>> M.identity_map().preimage(M) is M True - Another trivial case: - sage: M = Manifold(2, 'M', structure='topological') sage: X.<x,y> = M.chart() sage: D1 = M.open_subset('D1', coord_def={X: x^2+y^2<1}) # the open unit disk sage: D2 = M.open_subset('D2', coord_def={X: x^2+y^2<4}) sage: f = Hom(D1,D2)({(X.restrict(D1), X.restrict(D2)): (2*x, 2*y)}, name='f') sage: f.preimage(D2) Open subset D1 of the 2-dimensional topological manifold M sage: f.preimage(M) Open subset D1 of the 2-dimensional topological manifold M - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> X = M.chart(names=('x', 'y',)); (x, y,) = X._first_ngens(2) >>> D1 = M.open_subset('D1', coord_def={X: x**Integer(2)+y**Integer(2)<Integer(1)}) # the open unit disk >>> D2 = M.open_subset('D2', coord_def={X: x**Integer(2)+y**Integer(2)<Integer(4)}) >>> f = Hom(D1,D2)({(X.restrict(D1), X.restrict(D2)): (Integer(2)*x, Integer(2)*y)}, name='f') >>> f.preimage(D2) Open subset D1 of the 2-dimensional topological manifold M >>> f.preimage(M) Open subset D1 of the 2-dimensional topological manifold M 
 - pullback(codomain_subset, name=None, latex_name=None)[source]¶
- Return the preimage of - codomain_subsetunder- self.- An alias is - pullback().- INPUT: - codomain_subset– an instance of- ManifoldSubset
- name– string; name (symbol) given to the subset
- latex_name– string (default:- None); LaTeX symbol to denote the subset; if none are provided, it is set to- name
 - OUTPUT: - either a - TopologicalManifoldor a- ManifoldSubsetPullback
 - EXAMPLES: - sage: R = Manifold(1, 'R', structure='topological') # field R sage: T.<t> = R.chart() # canonical chart on R sage: R2 = Manifold(2, 'R^2', structure='topological') # R^2 sage: c_xy.<x,y> = R2.chart() # Cartesian coordinates on R^2 sage: Phi = R.continuous_map(R2, [cos(t), sin(t)], name='Phi'); Phi Continuous map Phi from the 1-dimensional topological manifold R to the 2-dimensional topological manifold R^2 sage: Q1 = R2.open_subset('Q1', coord_def={c_xy: [x>0, y>0]}); Q1 Open subset Q1 of the 2-dimensional topological manifold R^2 sage: Phi_inv_Q1 = Phi.preimage(Q1); Phi_inv_Q1 Subset Phi_inv_Q1 of the 1-dimensional topological manifold R sage: R.point([pi/4]) in Phi_inv_Q1 True sage: R.point([0]) in Phi_inv_Q1 False sage: R.point([3*pi/4]) in Phi_inv_Q1 False - >>> from sage.all import * >>> R = Manifold(Integer(1), 'R', structure='topological') # field R >>> T = R.chart(names=('t',)); (t,) = T._first_ngens(1)# canonical chart on R >>> R2 = Manifold(Integer(2), 'R^2', structure='topological') # R^2 >>> c_xy = R2.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# Cartesian coordinates on R^2 >>> Phi = R.continuous_map(R2, [cos(t), sin(t)], name='Phi'); Phi Continuous map Phi from the 1-dimensional topological manifold R to the 2-dimensional topological manifold R^2 >>> Q1 = R2.open_subset('Q1', coord_def={c_xy: [x>Integer(0), y>Integer(0)]}); Q1 Open subset Q1 of the 2-dimensional topological manifold R^2 >>> Phi_inv_Q1 = Phi.preimage(Q1); Phi_inv_Q1 Subset Phi_inv_Q1 of the 1-dimensional topological manifold R >>> R.point([pi/Integer(4)]) in Phi_inv_Q1 True >>> R.point([Integer(0)]) in Phi_inv_Q1 False >>> R.point([Integer(3)*pi/Integer(4)]) in Phi_inv_Q1 False - The identity map is handled specially: - sage: M = Manifold(2, 'M', structure='topological') sage: X.<x,y> = M.chart() sage: M.identity_map().preimage(M) 2-dimensional topological manifold M sage: M.identity_map().preimage(M) is M True - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> X = M.chart(names=('x', 'y',)); (x, y,) = X._first_ngens(2) >>> M.identity_map().preimage(M) 2-dimensional topological manifold M >>> M.identity_map().preimage(M) is M True - Another trivial case: - sage: M = Manifold(2, 'M', structure='topological') sage: X.<x,y> = M.chart() sage: D1 = M.open_subset('D1', coord_def={X: x^2+y^2<1}) # the open unit disk sage: D2 = M.open_subset('D2', coord_def={X: x^2+y^2<4}) sage: f = Hom(D1,D2)({(X.restrict(D1), X.restrict(D2)): (2*x, 2*y)}, name='f') sage: f.preimage(D2) Open subset D1 of the 2-dimensional topological manifold M sage: f.preimage(M) Open subset D1 of the 2-dimensional topological manifold M - >>> from sage.all import * >>> M = Manifold(Integer(2), 'M', structure='topological') >>> X = M.chart(names=('x', 'y',)); (x, y,) = X._first_ngens(2) >>> D1 = M.open_subset('D1', coord_def={X: x**Integer(2)+y**Integer(2)<Integer(1)}) # the open unit disk >>> D2 = M.open_subset('D2', coord_def={X: x**Integer(2)+y**Integer(2)<Integer(4)}) >>> f = Hom(D1,D2)({(X.restrict(D1), X.restrict(D2)): (Integer(2)*x, Integer(2)*y)}, name='f') >>> f.preimage(D2) Open subset D1 of the 2-dimensional topological manifold M >>> f.preimage(M) Open subset D1 of the 2-dimensional topological manifold M 
 - restrict(subdomain, subcodomain=None)[source]¶
- Restriction of - selfto some open subset of its domain of definition.- INPUT: - subdomain–- TopologicalManifold; an open subset of the domain of- self
- subcodomain– (default:- None) an open subset of the codomain of- self; if- None, the codomain of- selfis assumed
 - OUTPUT: - a - ContinuousMapthat is the restriction of- selfto- subdomain
 - EXAMPLES: - Restriction to an annulus of a homeomorphism between the open unit disk and \(\RR^2\): - sage: M = Manifold(2, 'R^2', structure='topological') # R^2 sage: c_xy.<x,y> = M.chart() # Cartesian coord. on R^2 sage: D = M.open_subset('D', coord_def={c_xy: x^2+y^2<1}) # the open unit disk sage: Phi = D.continuous_map(M, [x/sqrt(1-x^2-y^2), y/sqrt(1-x^2-y^2)], ....: name='Phi', latex_name=r'\Phi') sage: Phi.display() Phi: D → R^2 (x, y) ↦ (x, y) = (x/sqrt(-x^2 - y^2 + 1), y/sqrt(-x^2 - y^2 + 1)) sage: c_xy_D = c_xy.restrict(D) sage: U = D.open_subset('U', coord_def={c_xy_D: x^2+y^2>1/2}) # the annulus 1/2 < r < 1 sage: Phi.restrict(U) Continuous map Phi from the Open subset U of the 2-dimensional topological manifold R^2 to the 2-dimensional topological manifold R^2 sage: Phi.restrict(U).parent() Set of Morphisms from Open subset U of the 2-dimensional topological manifold R^2 to 2-dimensional topological manifold R^2 in Category of manifolds over Real Field with 53 bits of precision sage: Phi.domain() Open subset D of the 2-dimensional topological manifold R^2 sage: Phi.restrict(U).domain() Open subset U of the 2-dimensional topological manifold R^2 sage: Phi.restrict(U).display() Phi: U → R^2 (x, y) ↦ (x, y) = (x/sqrt(-x^2 - y^2 + 1), y/sqrt(-x^2 - y^2 + 1)) - >>> from sage.all import * >>> M = Manifold(Integer(2), 'R^2', structure='topological') # R^2 >>> c_xy = M.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# Cartesian coord. on R^2 >>> D = M.open_subset('D', coord_def={c_xy: x**Integer(2)+y**Integer(2)<Integer(1)}) # the open unit disk >>> Phi = D.continuous_map(M, [x/sqrt(Integer(1)-x**Integer(2)-y**Integer(2)), y/sqrt(Integer(1)-x**Integer(2)-y**Integer(2))], ... name='Phi', latex_name=r'\Phi') >>> Phi.display() Phi: D → R^2 (x, y) ↦ (x, y) = (x/sqrt(-x^2 - y^2 + 1), y/sqrt(-x^2 - y^2 + 1)) >>> c_xy_D = c_xy.restrict(D) >>> U = D.open_subset('U', coord_def={c_xy_D: x**Integer(2)+y**Integer(2)>Integer(1)/Integer(2)}) # the annulus 1/2 < r < 1 >>> Phi.restrict(U) Continuous map Phi from the Open subset U of the 2-dimensional topological manifold R^2 to the 2-dimensional topological manifold R^2 >>> Phi.restrict(U).parent() Set of Morphisms from Open subset U of the 2-dimensional topological manifold R^2 to 2-dimensional topological manifold R^2 in Category of manifolds over Real Field with 53 bits of precision >>> Phi.domain() Open subset D of the 2-dimensional topological manifold R^2 >>> Phi.restrict(U).domain() Open subset U of the 2-dimensional topological manifold R^2 >>> Phi.restrict(U).display() Phi: U → R^2 (x, y) ↦ (x, y) = (x/sqrt(-x^2 - y^2 + 1), y/sqrt(-x^2 - y^2 + 1)) - The result is cached: - sage: Phi.restrict(U) is Phi.restrict(U) True - >>> from sage.all import * >>> Phi.restrict(U) is Phi.restrict(U) True - The restriction of the identity map: - sage: id = D.identity_map() ; id Identity map Id_D of the Open subset D of the 2-dimensional topological manifold R^2 sage: id.restrict(U) Identity map Id_U of the Open subset U of the 2-dimensional topological manifold R^2 sage: id.restrict(U) is U.identity_map() True - >>> from sage.all import * >>> id = D.identity_map() ; id Identity map Id_D of the Open subset D of the 2-dimensional topological manifold R^2 >>> id.restrict(U) Identity map Id_U of the Open subset U of the 2-dimensional topological manifold R^2 >>> id.restrict(U) is U.identity_map() True - The codomain can be restricted (i.e. made tighter): - sage: Phi = D.continuous_map(M, [x/sqrt(1+x^2+y^2), y/sqrt(1+x^2+y^2)]) sage: Phi Continuous map from the Open subset D of the 2-dimensional topological manifold R^2 to the 2-dimensional topological manifold R^2 sage: Phi.restrict(D, subcodomain=D) Continuous map from the Open subset D of the 2-dimensional topological manifold R^2 to itself - >>> from sage.all import * >>> Phi = D.continuous_map(M, [x/sqrt(Integer(1)+x**Integer(2)+y**Integer(2)), y/sqrt(Integer(1)+x**Integer(2)+y**Integer(2))]) >>> Phi Continuous map from the Open subset D of the 2-dimensional topological manifold R^2 to the 2-dimensional topological manifold R^2 >>> Phi.restrict(D, subcodomain=D) Continuous map from the Open subset D of the 2-dimensional topological manifold R^2 to itself 
 - set_expr(chart1, chart2, coord_functions)[source]¶
- Set a new coordinate representation of - self.- The expressions with respect to other charts are deleted, in order to avoid any inconsistency. To keep them, use - add_expr()instead.- INPUT: - chart1– chart for the coordinates on the domain of- self
- chart2– chart for the coordinates on the codomain of- self
- coord_functions– the coordinate symbolic expression of the map in the above charts: list (or tuple) of the coordinates of the image expressed in terms of the coordinates of the considered point; if the dimension of the arrival manifold is 1, a single coordinate expression can be passed instead of a tuple with a single element
 - EXAMPLES: - Polar representation of a planar rotation initially defined in Cartesian coordinates: - sage: M = Manifold(2, 'R^2', latex_name=r'\RR^2', structure='topological') # the Euclidean plane R^2 sage: c_xy.<x,y> = M.chart() # Cartesian coordinate on R^2 sage: U = M.open_subset('U', coord_def={c_xy: (y!=0, x<0)}) # the complement of the segment y=0 and x>0 sage: c_cart = c_xy.restrict(U) # Cartesian coordinates on U sage: c_spher.<r,ph> = U.chart(r'r:(0,+oo) ph:(0,2*pi):\phi') # spherical coordinates on U - >>> from sage.all import * >>> M = Manifold(Integer(2), 'R^2', latex_name=r'\RR^2', structure='topological') # the Euclidean plane R^2 >>> c_xy = M.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# Cartesian coordinate on R^2 >>> U = M.open_subset('U', coord_def={c_xy: (y!=Integer(0), x<Integer(0))}) # the complement of the segment y=0 and x>0 >>> c_cart = c_xy.restrict(U) # Cartesian coordinates on U >>> c_spher = U.chart(r'r:(0,+oo) ph:(0,2*pi):\phi', names=('r', 'ph',)); (r, ph,) = c_spher._first_ngens(2)# spherical coordinates on U - Links between spherical coordinates and Cartesian ones: - sage: ch_cart_spher = c_cart.transition_map(c_spher, ....: [sqrt(x*x+y*y), atan2(y,x)]) sage: ch_cart_spher.set_inverse(r*cos(ph), r*sin(ph)) Check of the inverse coordinate transformation: x == x *passed* y == y *passed* r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** NB: a failed report can reflect a mere lack of simplification. sage: rot = U.continuous_map(U, ((x - sqrt(3)*y)/2, (sqrt(3)*x + y)/2), ....: name='R') sage: rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - >>> from sage.all import * >>> ch_cart_spher = c_cart.transition_map(c_spher, ... [sqrt(x*x+y*y), atan2(y,x)]) >>> ch_cart_spher.set_inverse(r*cos(ph), r*sin(ph)) Check of the inverse coordinate transformation: x == x *passed* y == y *passed* r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** NB: a failed report can reflect a mere lack of simplification. >>> rot = U.continuous_map(U, ((x - sqrt(Integer(3))*y)/Integer(2), (sqrt(Integer(3))*x + y)/Integer(2)), ... name='R') >>> rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - Let us use the method - set_expr()to set the spherical-coordinate expression by hand:- sage: rot.set_expr(c_spher, c_spher, (r, ph+pi/3)) sage: rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, 1/3*pi + ph) - >>> from sage.all import * >>> rot.set_expr(c_spher, c_spher, (r, ph+pi/Integer(3))) >>> rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, 1/3*pi + ph) - The expression in Cartesian coordinates has been erased: - sage: rot._coord_expression {(Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot._coord_expression {(Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - It is recovered (thanks to the known change of coordinates) by a call to - display():- sage: rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) sage: rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) >>> rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} 
 - set_expression(chart1, chart2, coord_functions)[source]¶
- Set a new coordinate representation of - self.- The expressions with respect to other charts are deleted, in order to avoid any inconsistency. To keep them, use - add_expr()instead.- INPUT: - chart1– chart for the coordinates on the domain of- self
- chart2– chart for the coordinates on the codomain of- self
- coord_functions– the coordinate symbolic expression of the map in the above charts: list (or tuple) of the coordinates of the image expressed in terms of the coordinates of the considered point; if the dimension of the arrival manifold is 1, a single coordinate expression can be passed instead of a tuple with a single element
 - EXAMPLES: - Polar representation of a planar rotation initially defined in Cartesian coordinates: - sage: M = Manifold(2, 'R^2', latex_name=r'\RR^2', structure='topological') # the Euclidean plane R^2 sage: c_xy.<x,y> = M.chart() # Cartesian coordinate on R^2 sage: U = M.open_subset('U', coord_def={c_xy: (y!=0, x<0)}) # the complement of the segment y=0 and x>0 sage: c_cart = c_xy.restrict(U) # Cartesian coordinates on U sage: c_spher.<r,ph> = U.chart(r'r:(0,+oo) ph:(0,2*pi):\phi') # spherical coordinates on U - >>> from sage.all import * >>> M = Manifold(Integer(2), 'R^2', latex_name=r'\RR^2', structure='topological') # the Euclidean plane R^2 >>> c_xy = M.chart(names=('x', 'y',)); (x, y,) = c_xy._first_ngens(2)# Cartesian coordinate on R^2 >>> U = M.open_subset('U', coord_def={c_xy: (y!=Integer(0), x<Integer(0))}) # the complement of the segment y=0 and x>0 >>> c_cart = c_xy.restrict(U) # Cartesian coordinates on U >>> c_spher = U.chart(r'r:(0,+oo) ph:(0,2*pi):\phi', names=('r', 'ph',)); (r, ph,) = c_spher._first_ngens(2)# spherical coordinates on U - Links between spherical coordinates and Cartesian ones: - sage: ch_cart_spher = c_cart.transition_map(c_spher, ....: [sqrt(x*x+y*y), atan2(y,x)]) sage: ch_cart_spher.set_inverse(r*cos(ph), r*sin(ph)) Check of the inverse coordinate transformation: x == x *passed* y == y *passed* r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** NB: a failed report can reflect a mere lack of simplification. sage: rot = U.continuous_map(U, ((x - sqrt(3)*y)/2, (sqrt(3)*x + y)/2), ....: name='R') sage: rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - >>> from sage.all import * >>> ch_cart_spher = c_cart.transition_map(c_spher, ... [sqrt(x*x+y*y), atan2(y,x)]) >>> ch_cart_spher.set_inverse(r*cos(ph), r*sin(ph)) Check of the inverse coordinate transformation: x == x *passed* y == y *passed* r == r *passed* ph == arctan2(r*sin(ph), r*cos(ph)) **failed** NB: a failed report can reflect a mere lack of simplification. >>> rot = U.continuous_map(U, ((x - sqrt(Integer(3))*y)/Integer(2), (sqrt(Integer(3))*x + y)/Integer(2)), ... name='R') >>> rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) - Let us use the method - set_expr()to set the spherical-coordinate expression by hand:- sage: rot.set_expr(c_spher, c_spher, (r, ph+pi/3)) sage: rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, 1/3*pi + ph) - >>> from sage.all import * >>> rot.set_expr(c_spher, c_spher, (r, ph+pi/Integer(3))) >>> rot.display(c_spher, c_spher) R: U → U (r, ph) ↦ (r, 1/3*pi + ph) - The expression in Cartesian coordinates has been erased: - sage: rot._coord_expression {(Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot._coord_expression {(Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - It is recovered (thanks to the known change of coordinates) by a call to - display():- sage: rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) sage: rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))} - >>> from sage.all import * >>> rot.display(c_cart, c_cart) R: U → U (x, y) ↦ (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) >>> rot._coord_expression # random (dictionary output) {(Chart (U, (x, y)), Chart (U, (x, y))): Coordinate functions (-1/2*sqrt(3)*y + 1/2*x, 1/2*sqrt(3)*x + 1/2*y) on the Chart (U, (x, y)), (Chart (U, (r, ph)), Chart (U, (r, ph))): Coordinate functions (r, 1/3*pi + ph) on the Chart (U, (r, ph))}