Vector Frames¶
The class VectorFrame
implements vector frames on differentiable
manifolds.
By vector frame, it is meant a field \(e\) on some
differentiable manifold \(U\) endowed with a differentiable map
\(\Phi: U \rightarrow M\) to a differentiable manifold \(M\) such that for each
\(p\in U\), \(e(p)\) is a vector basis of the tangent space \(T_{\Phi(p)}M\).
The standard case of a vector frame on \(U\) corresponds to \(U = M\) and \(\Phi = \mathrm{Id}_M\). Other common cases are \(\Phi\) being an immersion and \(\Phi\) being a curve in \(M\) (\(U\) is then an open interval of \(\RR\)).
A derived class of VectorFrame
is CoordFrame
;
it regards the vector frames associated with a chart, i.e. the
socalled coordinate bases.
The vector frame duals, i.e. the coframes, are implemented via the class
CoFrame
. The derived class CoordCoFrame
is devoted to
coframes deriving from a chart.
AUTHORS:
 Eric Gourgoulhon, Michal Bejger (20132015): initial version
 Travis Scrimshaw (2016): review tweaks
REFERENCES:
EXAMPLES:
Setting a vector frame on a 3dimensional manifold:
sage: M = Manifold(3, 'M')
sage: c_xyz.<x,y,z> = M.chart()
sage: e = M.vector_frame('e') ; e
Vector frame (M, (e_0,e_1,e_2))
sage: latex(e)
\left(M, \left(e_{0},e_{1},e_{2}\right)\right)
The first frame defined on a manifold is its default frame; in the present
case it is the coordinate frame defined when introducing the chart
c_xyz
:
sage: M.default_frame()
Coordinate frame (M, (d/dx,d/dy,d/dz))
The default frame can be changed via the method
set_default_frame()
:
sage: M.set_default_frame(e)
sage: M.default_frame()
Vector frame (M, (e_0,e_1,e_2))
The elements of a vector frame are vector fields on the manifold:
sage: [e[i] for i in M.irange()]
[Vector field e_0 on the 3dimensional differentiable manifold M,
Vector field e_1 on the 3dimensional differentiable manifold M,
Vector field e_2 on the 3dimensional differentiable manifold M]
Each element can be accessed by its index:
sage: e[0]
Vector field e_0 on the 3dimensional differentiable manifold M
The index range depends on the starting index defined on the manifold:
sage: M = Manifold(3, 'M', start_index=1)
sage: c_xyz.<x,y,z> = M.chart()
sage: e = M.vector_frame('e')
sage: [e[i] for i in M.irange()]
[Vector field e_1 on the 3dimensional differentiable manifold M,
Vector field e_2 on the 3dimensional differentiable manifold M,
Vector field e_3 on the 3dimensional differentiable manifold M]
sage: e[1], e[2], e[3]
(Vector field e_1 on the 3dimensional differentiable manifold M,
Vector field e_2 on the 3dimensional differentiable manifold M,
Vector field e_3 on the 3dimensional differentiable manifold M)
Let us check that the vector fields e[i]
are the frame vectors from
their components with respect to the frame \(e\):
sage: e[1].comp(e)[:]
[1, 0, 0]
sage: e[2].comp(e)[:]
[0, 1, 0]
sage: e[3].comp(e)[:]
[0, 0, 1]
Defining a vector frame on a manifold automatically creates the dual coframe, which bares the same name (here \(e\)):
sage: M.coframes()
[Coordinate coframe (M, (dx,dy,dz)), Coframe (M, (e^1,e^2,e^3))]
sage: f = M.coframes()[1] ; f
Coframe (M, (e^1,e^2,e^3))
Each element of the coframe is a 1form:
sage: f[1], f[2], f[3]
(1form e^1 on the 3dimensional differentiable manifold M,
1form e^2 on the 3dimensional differentiable manifold M,
1form e^3 on the 3dimensional differentiable manifold M)
sage: latex(f[1]), latex(f[2]), latex(f[3])
(e^{1}, e^{2}, e^{3})
Let us check that the coframe \((e^i)\) is indeed the dual of the vector frame \((e_i)\):
sage: f[1](e[1]) # the 1form e^1 applied to the vector field e_1
Scalar field e^1(e_1) on the 3dimensional differentiable manifold M
sage: f[1](e[1]).expr() # the explicit expression of e^1(e_1)
1
sage: f[1](e[1]).expr(), f[1](e[2]).expr(), f[1](e[3]).expr()
(1, 0, 0)
sage: f[2](e[1]).expr(), f[2](e[2]).expr(), f[2](e[3]).expr()
(0, 1, 0)
sage: f[3](e[1]).expr(), f[3](e[2]).expr(), f[3](e[3]).expr()
(0, 0, 1)
The coordinate frame associated to spherical coordinates of the sphere \(S^2\):
sage: M = Manifold(2, 'S^2', start_index=1) # Part of S^2 covered by spherical coord.
sage: c_spher.<th,ph> = M.chart(r'th:[0,pi]:\theta ph:[0,2*pi):\phi')
sage: b = M.default_frame() ; b
Coordinate frame (S^2, (d/dth,d/dph))
sage: b[1]
Vector field d/dth on the 2dimensional differentiable manifold S^2
sage: b[2]
Vector field d/dph on the 2dimensional differentiable manifold S^2
The orthonormal frame constructed from the coordinate frame:
sage: change_frame = M.automorphism_field()
sage: change_frame[:] = [[1,0], [0, 1/sin(th)]]
sage: e = b.new_frame(change_frame, 'e') ; e
Vector frame (S^2, (e_1,e_2))
sage: e[1][:]
[1, 0]
sage: e[2][:]
[0, 1/sin(th)]
The changeofframe automorphisms and their matrices:
sage: M.change_of_frame(c_spher.frame(), e)
Field of tangentspace automorphisms on the 2dimensional
differentiable manifold S^2
sage: M.change_of_frame(c_spher.frame(), e)[:]
[ 1 0]
[ 0 1/sin(th)]
sage: M.change_of_frame(e, c_spher.frame())
Field of tangentspace automorphisms on the 2dimensional
differentiable manifold S^2
sage: M.change_of_frame(e, c_spher.frame())[:]
[ 1 0]
[ 0 sin(th)]

class
sage.manifolds.differentiable.vectorframe.
CoFrame
(frame, symbol, latex_symbol=None)¶ Bases:
sage.tensor.modules.free_module_basis.FreeModuleCoBasis
Coframe on a differentiable manifold.
By coframe, it is meant a field \(f\) on some differentiable manifold \(U\) endowed with a differentiable map \(\Phi: U \rightarrow M\) to a differentiable manifold \(M\) such that for each \(p\in U\), \(f(p)\) is a basis of the vector space \(T^*_{\Phi(p)}M\) (the dual to the tangent space \(T_{\Phi(p)}M\)).
The standard case of a coframe on \(U\) corresponds to \(U = M\) and \(\Phi = \mathrm{Id}_M\). Other common cases are \(\Phi\) being an immersion and \(\Phi\) being a curve in \(M\) (\(U\) is then an open interval of \(\RR\)).
INPUT:
frame
– the vector frame dual to the coframesymbol
– a letter (of a few letters) to denote a generic 1form in the coframelatex_symbol
– (default:None
) symbol to denote a generic 1form in the coframe; ifNone
, the value ofsymbol
is used
EXAMPLES:
Coframe on a 3dimensional manifold:
sage: M = Manifold(3, 'M', start_index=1) sage: c_xyz.<x,y,z> = M.chart() sage: v = M.vector_frame('v') sage: from sage.manifolds.differentiable.vectorframe import CoFrame sage: e = CoFrame(v, 'e') ; e Coframe (M, (e^1,e^2,e^3))
Instead of importing CoFrame in the global namespace, the coframe can be obtained by means of the method
dual_basis()
; the symbol is then the same as that of the frame:sage: a = v.dual_basis() ; a Coframe (M, (v^1,v^2,v^3)) sage: a[1] == e[1] True sage: a[1] is e[1] False sage: e[1].display(v) e^1 = v^1
The 1forms composing the coframe are obtained via the operator
[]
:sage: e[1], e[2], e[3] (1form e^1 on the 3dimensional differentiable manifold M, 1form e^2 on the 3dimensional differentiable manifold M, 1form e^3 on the 3dimensional differentiable manifold M)
Checking that \(e\) is the dual of \(v\):
sage: e[1](v[1]).expr(), e[1](v[2]).expr(), e[1](v[3]).expr() (1, 0, 0) sage: e[2](v[1]).expr(), e[2](v[2]).expr(), e[2](v[3]).expr() (0, 1, 0) sage: e[3](v[1]).expr(), e[3](v[2]).expr(), e[3](v[3]).expr() (0, 0, 1)

at
(point)¶ Return the value of
self
at a given point on the manifold, this value being a basis of the dual of the tangent space at the point.INPUT:
point
–ManifoldPoint
; point \(p\) in the domain \(U\) of the coframe (denoted \(f\) hereafter)
OUTPUT:
FreeModuleCoBasis
representing the basis \(f(p)\) of the vector space \(T^*_{\Phi(p)} M\), dual to the tangent space \(T_{\Phi(p)} M\), where \(\Phi: U \to M\) is the differentiable map associated with \(f\) (possibly \(\Phi = \mathrm{Id}_U\))
EXAMPLES:
Cobasis of a tangent space on a 2dimensional manifold:
sage: M = Manifold(2, 'M') sage: X.<x,y> = M.chart() sage: p = M.point((1,2), name='p') sage: f = X.coframe() ; f Coordinate coframe (M, (dx,dy)) sage: fp = f.at(p) ; fp Dual basis (dx,dy) on the Tangent space at Point p on the 2dimensional differentiable manifold M sage: type(fp) <class 'sage.tensor.modules.free_module_basis.FreeModuleCoBasis'> sage: fp[0] Linear form dx on the Tangent space at Point p on the 2dimensional differentiable manifold M sage: fp[1] Linear form dy on the Tangent space at Point p on the 2dimensional differentiable manifold M sage: fp is X.frame().at(p).dual_basis() True

class
sage.manifolds.differentiable.vectorframe.
CoordCoFrame
(coord_frame)¶ Bases:
sage.manifolds.differentiable.vectorframe.CoFrame
Coordinate coframe on a differentiable manifold.
By coordinate coframe, it is meant the \(n\)tuple of the differentials of the coordinates of some chart on the manifold, with \(n\) being the manifold’s dimension.
INPUT:
coord_frame
– coordinate frame dual to the coordinate coframe
EXAMPLES:
Coordinate coframe on a 3dimensional manifold:
sage: M = Manifold(3, 'M', start_index=1) sage: c_xyz.<x,y,z> = M.chart() sage: M.frames() [Coordinate frame (M, (d/dx,d/dy,d/dz))] sage: M.coframes() [Coordinate coframe (M, (dx,dy,dz))] sage: dX = M.coframes()[0] ; dX Coordinate coframe (M, (dx,dy,dz))
The 1forms composing the coframe are obtained via the operator
[]
:sage: dX[1] 1form dx on the 3dimensional differentiable manifold M sage: dX[2] 1form dy on the 3dimensional differentiable manifold M sage: dX[3] 1form dz on the 3dimensional differentiable manifold M sage: dX[1][:] [1, 0, 0] sage: dX[2][:] [0, 1, 0] sage: dX[3][:] [0, 0, 1]
The coframe is the dual of the coordinate frame:
sage: e = c_xyz.frame() ; e Coordinate frame (M, (d/dx,d/dy,d/dz)) sage: dX[1](e[1]).expr(), dX[1](e[2]).expr(), dX[1](e[3]).expr() (1, 0, 0) sage: dX[2](e[1]).expr(), dX[2](e[2]).expr(), dX[2](e[3]).expr() (0, 1, 0) sage: dX[3](e[1]).expr(), dX[3](e[2]).expr(), dX[3](e[3]).expr() (0, 0, 1)
Each 1form of a coordinate coframe is closed:
sage: dX[1].exterior_derivative() 2form ddx on the 3dimensional differentiable manifold M sage: dX[1].exterior_derivative() == 0 True

class
sage.manifolds.differentiable.vectorframe.
CoordFrame
(chart)¶ Bases:
sage.manifolds.differentiable.vectorframe.VectorFrame
Coordinate frame on a differentiable manifold.
By coordinate frame, it is meant a vector frame on a differentiable manifold \(M\) that is associated to a coordinate chart on \(M\).
INPUT:
chart
– the chart defining the coordinates
EXAMPLES:
The coordinate frame associated to spherical coordinates of the sphere \(S^2\):
sage: M = Manifold(2, 'S^2', start_index=1) # Part of S^2 covered by spherical coord. sage: M.chart(r'th:[0,pi]:\theta ph:[0,2*pi):\phi') Chart (S^2, (th, ph)) sage: b = M.default_frame() sage: b Coordinate frame (S^2, (d/dth,d/dph)) sage: b[1] Vector field d/dth on the 2dimensional differentiable manifold S^2 sage: b[2] Vector field d/dph on the 2dimensional differentiable manifold S^2 sage: latex(b) \left(S^2, \left(\frac{\partial}{\partial {\theta} },\frac{\partial}{\partial {\phi} }\right)\right)

chart
()¶ Return the chart defining this coordinate frame.
EXAMPLES:
sage: M = Manifold(2, 'M') sage: X.<x,y> = M.chart() sage: e = X.frame() sage: e.chart() Chart (M, (x, y)) sage: U = M.open_subset('U', coord_def={X: x>0}) sage: e.restrict(U).chart() Chart (U, (x, y))

structure_coeff
()¶ Return the structure coefficients associated to
self
.\(n\) being the manifold’s dimension, the structure coefficients of the frame \((e_i)\) are the \(n^3\) scalar fields \(C^k_{\ \, ij}\) defined by
\[[e_i, e_j] = C^k_{\ \, ij} e_k.\]In the present case, since \((e_i)\) is a coordinate frame, \(C^k_{\ \, ij}=0\).
OUTPUT:
 the structure coefficients \(C^k_{\ \, ij}\), as a vanishing instance
of
CompWithSym
with 3 indices ordered as \((k,i,j)\)
EXAMPLES:
Structure coefficients of the coordinate frame associated to spherical coordinates in the Euclidean space \(\RR^3\):
sage: M = Manifold(3, 'R^3', r'\RR^3', start_index=1) # Part of R^3 covered by spherical coord. sage: c_spher = M.chart(r'r:(0,+oo) th:(0,pi):\theta ph:(0,2*pi):\phi') sage: b = M.default_frame() ; b Coordinate frame (R^3, (d/dr,d/dth,d/dph)) sage: c = b.structure_coeff() ; c 3indices components w.r.t. Coordinate frame (R^3, (d/dr,d/dth,d/dph)), with antisymmetry on the index positions (1, 2) sage: c == 0 True
 the structure coefficients \(C^k_{\ \, ij}\), as a vanishing instance
of

class
sage.manifolds.differentiable.vectorframe.
VectorFrame
(vector_field_module, symbol, latex_symbol=None, from_frame=None)¶ Bases:
sage.tensor.modules.free_module_basis.FreeModuleBasis
Vector frame on a differentiable manifold.
By vector frame, it is meant a field \(e\) on some differentiable manifold \(U\) endowed with a differentiable map \(\Phi: U\rightarrow M\) to a differentiable manifold \(M\) such that for each \(p\in U\), \(e(p)\) is a vector basis of the tangent space \(T_{\Phi(p)}M\).
The standard case of a vector frame on \(U\) corresponds to \(U=M\) and \(\Phi = \mathrm{Id}_M\). Other common cases are \(\Phi\) being an immersion and \(\Phi\) being a curve in \(M\) (\(U\) is then an open interval of \(\RR\)).
For each instanciation of a vector frame, a coframe is automatically created, as an instance of the class
CoFrame
. It is returned by the methodcoframe()
.INPUT:
vector_field_module
– free module \(\mathfrak{X}(U, \Phi)\) of vector fields along \(U\) with values on \(M \supset \Phi(U)\)symbol
– a letter (of a few letters) to denote a generic vector of the frame; can be set to None if the parameterfrom_frame
is filledlatex_symbol
– (default:None
) symbol to denote a generic vector of the frame; ifNone
, the value ofsymbol
is usedfrom_frame
– (default:None
) vector frame \(\tilde e\) on the codomain \(M\) of the destination map \(\Phi\); the constructed frame \(e\) is then such that \(\forall p \in U, e(p) = \tilde{e}(\Phi(p))\)
EXAMPLES:
Setting a vector frame on a 3dimensional manifold:
sage: M = Manifold(3, 'M') sage: c_xyz.<x,y,z> = M.chart() sage: e = M.vector_frame('e') ; e Vector frame (M, (e_0,e_1,e_2)) sage: latex(e) \left(M, \left(e_{0},e_{1},e_{2}\right)\right)
The LaTeX symbol can be specified:
sage: e = M.vector_frame('E', r"\epsilon") sage: latex(e) \left(M, \left(\epsilon_{0},\epsilon_{1},\epsilon_{2}\right)\right)
Example with a nontrivial map \(\Phi\); a vector frame along a curve:
sage: U = Manifold(1, 'U') # open interval (1,1) as a 1dimensional manifold sage: T.<t> = U.chart('t:(1,1)') # canonical chart on U sage: Phi = U.diff_map(M, [cos(t), sin(t), t], name='Phi', ....: latex_name=r'\Phi') sage: Phi Differentiable map Phi from the 1dimensional differentiable manifold U to the 3dimensional differentiable manifold M sage: f = U.vector_frame('f', dest_map=Phi) ; f Vector frame (U, (f_0,f_1,f_2)) with values on the 3dimensional differentiable manifold M sage: f.domain() 1dimensional differentiable manifold U sage: f.ambient_domain() 3dimensional differentiable manifold M
The value of the vector frame at a given point is a basis of the corresponding tangent space:
sage: p = U((0,), name='p') ; p Point p on the 1dimensional differentiable manifold U sage: f.at(p) Basis (f_0,f_1,f_2) on the Tangent space at Point Phi(p) on the 3dimensional differentiable manifold M
Vector frames are bases of free modules formed by vector fields:
sage: e.module() Free module X(M) of vector fields on the 3dimensional differentiable manifold M sage: e.module().base_ring() Algebra of differentiable scalar fields on the 3dimensional differentiable manifold M sage: e.module() is M.vector_field_module() True sage: e in M.vector_field_module().bases() True
sage: f.module() Free module X(U,Phi) of vector fields along the 1dimensional differentiable manifold U mapped into the 3dimensional differentiable manifold M sage: f.module().base_ring() Algebra of differentiable scalar fields on the 1dimensional differentiable manifold U sage: f.module() is U.vector_field_module(dest_map=Phi) True sage: f in U.vector_field_module(dest_map=Phi).bases() True

along
(mapping)¶ Return the vector frame deduced from the current frame via a differentiable map, the codomain of which is included in the domain of of the current frame.
If \(e\) is the current vector frame, \(V\) its domain and if \(\Phi: U \rightarrow V\) is a differentiable map from some differentiable manifold \(U\) to \(V\), the returned object is a vector frame \(\tilde e\) along \(U\) with values on \(V\) such that
\[\forall p \in U,\ \tilde e(p) = e(\Phi(p)).\]INPUT:
mapping
– differentiable map \(\Phi: U \rightarrow V\)
OUTPUT:
 vector frame \(\tilde e\) along \(U\) defined above.
EXAMPLES:
Vector frame along a curve:
sage: M = Manifold(2, 'M') sage: X.<x,y> = M.chart() sage: R = Manifold(1, 'R') # R as a 1dimensional manifold sage: T.<t> = R.chart() # canonical chart on R sage: Phi = R.diff_map(M, {(T,X): [cos(t), t]}, name='Phi', ....: latex_name=r'\Phi') ; Phi Differentiable map Phi from the 1dimensional differentiable manifold R to the 2dimensional differentiable manifold M sage: e = X.frame() ; e Coordinate frame (M, (d/dx,d/dy)) sage: te = e.along(Phi) ; te Vector frame (R, (d/dx,d/dy)) with values on the 2dimensional differentiable manifold M
Check of the formula \(\tilde e(p) = e(\Phi(p))\):
sage: p = R((pi,)) ; p Point on the 1dimensional differentiable manifold R sage: te[0].at(p) == e[0].at(Phi(p)) True sage: te[1].at(p) == e[1].at(Phi(p)) True
The result is cached:
sage: te is e.along(Phi) True

ambient_domain
()¶ Return the differentiable manifold in which
self
takes its values.The ambient domain is the codomain \(M\) of the differentiable map \(\Phi: U \rightarrow M\) associated with the frame.
OUTPUT:
 a
DifferentiableManifold
representing \(M\)
EXAMPLES:
sage: M = Manifold(2, 'M') sage: e = M.vector_frame('e') sage: e.ambient_domain() 2dimensional differentiable manifold M
In the present case, since \(\Phi\) is the identity map:
sage: e.ambient_domain() == e.domain() True
An example with a non trivial map \(\Phi\):
sage: U = Manifold(1, 'U') sage: T.<t> = U.chart() sage: X.<x,y> = M.chart() sage: Phi = U.diff_map(M, {(T,X): [cos(t), t]}, name='Phi', ....: latex_name=r'\Phi') ; Phi Differentiable map Phi from the 1dimensional differentiable manifold U to the 2dimensional differentiable manifold M sage: f = U.vector_frame('f', dest_map=Phi); f Vector frame (U, (f_0,f_1)) with values on the 2dimensional differentiable manifold M sage: f.ambient_domain() 2dimensional differentiable manifold M sage: f.domain() 1dimensional differentiable manifold U
 a

at
(point)¶ Return the value of
self
at a given point, this value being a basis of the tangent vector space at the point.INPUT:
point
–ManifoldPoint
; point \(p\) in the domain \(U\) of the vector frame (denoted \(e\) hereafter)
OUTPUT:
FreeModuleBasis
representing the basis \(e(p)\) of the tangent vector space \(T_{\Phi(p)} M\), where \(\Phi: U \to M\) is the differentiable map associated with \(e\) (possibly \(\Phi = \mathrm{Id}_U\))
EXAMPLES:
Basis of a tangent space to a 2dimensional manifold:
sage: M = Manifold(2, 'M') sage: X.<x,y> = M.chart() sage: p = M.point((1,2), name='p') sage: e = X.frame() ; e Coordinate frame (M, (d/dx,d/dy)) sage: ep = e.at(p) ; ep Basis (d/dx,d/dy) on the Tangent space at Point p on the 2dimensional differentiable manifold M sage: type(ep) <class 'sage.tensor.modules.free_module_basis.FreeModuleBasis'> sage: ep[0] Tangent vector d/dx at Point p on the 2dimensional differentiable manifold M sage: ep[1] Tangent vector d/dy at Point p on the 2dimensional differentiable manifold M
Note that the symbols used to denote the vectors are same as those for the vector fields of the frame. At this stage,
ep
is the unique basis on the tangent space atp
:sage: Tp = M.tangent_space(p) sage: Tp.bases() [Basis (d/dx,d/dy) on the Tangent space at Point p on the 2dimensional differentiable manifold M]
Let us consider a vector frame that is a not a coordinate one:
sage: aut = M.automorphism_field() sage: aut[:] = [[1+y^2, 0], [0, 2]] sage: f = e.new_frame(aut, 'f') ; f Vector frame (M, (f_0,f_1)) sage: fp = f.at(p) ; fp Basis (f_0,f_1) on the Tangent space at Point p on the 2dimensional differentiable manifold M
There are now two bases on the tangent space:
sage: Tp.bases() [Basis (d/dx,d/dy) on the Tangent space at Point p on the 2dimensional differentiable manifold M, Basis (f_0,f_1) on the Tangent space at Point p on the 2dimensional differentiable manifold M]
Moreover, the changes of bases in the tangent space have been computed from the known relation between the frames
e
andf
(field of automorphismsaut
defined above):sage: Tp.change_of_basis(ep, fp) Automorphism of the Tangent space at Point p on the 2dimensional differentiable manifold M sage: Tp.change_of_basis(ep, fp).display() 5 d/dx*dx + 2 d/dy*dy sage: Tp.change_of_basis(fp, ep) Automorphism of the Tangent space at Point p on the 2dimensional differentiable manifold M sage: Tp.change_of_basis(fp, ep).display() 1/5 d/dx*dx + 1/2 d/dy*dy
The dual bases:
sage: e.coframe() Coordinate coframe (M, (dx,dy)) sage: ep.dual_basis() Dual basis (dx,dy) on the Tangent space at Point p on the 2dimensional differentiable manifold M sage: ep.dual_basis() is e.coframe().at(p) True sage: f.coframe() Coframe (M, (f^0,f^1)) sage: fp.dual_basis() Dual basis (f^0,f^1) on the Tangent space at Point p on the 2dimensional differentiable manifold M sage: fp.dual_basis() is f.coframe().at(p) True

coframe
()¶ Return the coframe of
self
.EXAMPLES:
sage: M = Manifold(2, 'M') sage: e = M.vector_frame('e') sage: e.coframe() Coframe (M, (e^0,e^1)) sage: X.<x,y> = M.chart() sage: X.frame().coframe() Coordinate coframe (M, (dx,dy))

destination_map
()¶ Return the differential map associated to this vector frame.
Let \(e\) denote the vector frame; the differential map associated to it is the map \(\Phi: U\rightarrow M\) such that for each \(p \in U\), \(e(p)\) is a vector basis of the tangent space \(T_{\Phi(p)}M\).
OUTPUT:
 a
DiffMap
representing the differential map \(\Phi\)
EXAMPLES:
sage: M = Manifold(2, 'M') sage: e = M.vector_frame('e') sage: e.destination_map() Identity map Id_M of the 2dimensional differentiable manifold M
An example with a non trivial map \(\Phi\):
sage: U = Manifold(1, 'U') sage: T.<t> = U.chart() sage: X.<x,y> = M.chart() sage: Phi = U.diff_map(M, {(T,X): [cos(t), t]}, name='Phi', ....: latex_name=r'\Phi') ; Phi Differentiable map Phi from the 1dimensional differentiable manifold U to the 2dimensional differentiable manifold M sage: f = U.vector_frame('f', dest_map=Phi); f Vector frame (U, (f_0,f_1)) with values on the 2dimensional differentiable manifold M sage: f.destination_map() Differentiable map Phi from the 1dimensional differentiable manifold U to the 2dimensional differentiable manifold M
 a

domain
()¶ Return the domain on which
self
is defined.OUTPUT:
 a
DifferentiableManifold
; representing the domain of the vector frame
EXAMPLES:
sage: M = Manifold(2, 'M') sage: e = M.vector_frame('e') sage: e.domain() 2dimensional differentiable manifold M sage: U = M.open_subset('U') sage: f = e.restrict(U) sage: f.domain() Open subset U of the 2dimensional differentiable manifold M
 a

new_frame
(change_of_frame, symbol, latex_symbol=None)¶ Define a new vector frame from
self
.The new vector frame is defined from a field of tangentspace automorphisms; its domain is the same as that of the current frame.
INPUT:
change_of_frame
–AutomorphismFieldParal
; the field of tangent space automorphisms \(P\) that relates the current frame \((e_i)\) to the new frame \((n_i)\) according to \(n_i = P(e_i)\)symbol
– a letter (of a few letters) to denote a generic vector of the framelatex_symbol
– (default:None
) symbol to denote a generic vector of the frame; ifNone
, the value ofsymbol
is used
OUTPUT:
 the new frame \((n_i)\), as an instance of
VectorFrame
EXAMPLES:
Frame resulting from a \(\pi/3\)rotation in the Euclidean plane:
sage: M = Manifold(2, 'R^2') sage: c_xy.<x,y> = M.chart() sage: e = M.vector_frame('e') ; M.set_default_frame(e) sage: M._frame_changes {} sage: rot = M.automorphism_field() sage: rot[:] = [[sqrt(3)/2, 1/2], [1/2, sqrt(3)/2]] sage: n = e.new_frame(rot, 'n') sage: n[0][:] [1/2*sqrt(3), 1/2] sage: n[1][:] [1/2, 1/2*sqrt(3)] sage: a = M.change_of_frame(e,n) sage: a[:] [1/2*sqrt(3) 1/2] [ 1/2 1/2*sqrt(3)] sage: a == rot True sage: a is rot False sage: a._components # random (dictionary output) {Vector frame (R^2, (e_0,e_1)): 2indices components w.r.t. Vector frame (R^2, (e_0,e_1)), Vector frame (R^2, (n_0,n_1)): 2indices components w.r.t. Vector frame (R^2, (n_0,n_1))} sage: a.comp(n)[:] [1/2*sqrt(3) 1/2] [ 1/2 1/2*sqrt(3)] sage: a1 = M.change_of_frame(n,e) sage: a1[:] [1/2*sqrt(3) 1/2] [ 1/2 1/2*sqrt(3)] sage: a1 == rot.inverse() True sage: a1 is rot.inverse() False sage: e[0].comp(n)[:] [1/2*sqrt(3), 1/2] sage: e[1].comp(n)[:] [1/2, 1/2*sqrt(3)]

restrict
(subdomain)¶ Return the restriction of
self
to some open subset of its domain.If the restriction has not been defined yet, it is constructed here.
INPUT:
subdomain
– open subset \(V\) of the current frame domain \(U\)
OUTPUT:
 the restriction of the current frame to \(V\) as a
VectorFrame
EXAMPLES:
Restriction of a frame defined on \(\RR^2\) to the unit disk:
sage: M = Manifold(2, 'R^2', start_index=1) sage: c_cart.<x,y> = M.chart() # Cartesian coordinates on R^2 sage: a = M.automorphism_field() sage: a[:] = [[1y^2,0], [1+x^2, 2]] sage: e = c_cart.frame().new_frame(a, 'e') ; e Vector frame (R^2, (e_1,e_2)) sage: U = M.open_subset('U', coord_def={c_cart: x^2+y^2<1}) sage: e_U = e.restrict(U) ; e_U Vector frame (U, (e_1,e_2))
The vectors of the restriction have the same symbols as those of the original frame:
sage: e_U[1].display() e_1 = (y^2 + 1) d/dx + (x^2 + 1) d/dy sage: e_U[2].display() e_2 = 2 d/dy
They are actually the restrictions of the original frame vectors:
sage: e_U[1] is e[1].restrict(U) True sage: e_U[2] is e[2].restrict(U) True

structure_coeff
()¶ Evaluate the structure coefficients associated to
self
.\(n\) being the manifold’s dimension, the structure coefficients of the vector frame \((e_i)\) are the \(n^3\) scalar fields \(C^k_{\ \, ij}\) defined by
\[[e_i, e_j] = C^k_{\ \, ij} e_k\]OUTPUT:
 the structure coefficients \(C^k_{\ \, ij}\), as an instance of
CompWithSym
with 3 indices ordered as \((k,i,j)\).
EXAMPLES:
Structure coefficients of the orthonormal frame associated to spherical coordinates in the Euclidean space \(\RR^3\):
sage: M = Manifold(3, 'R^3', '\RR^3', start_index=1) # Part of R^3 covered by spherical coordinates sage: c_spher.<r,th,ph> = M.chart(r'r:(0,+oo) th:(0,pi):\theta ph:(0,2*pi):\phi') sage: ch_frame = M.automorphism_field() sage: ch_frame[1,1], ch_frame[2,2], ch_frame[3,3] = 1, 1/r, 1/(r*sin(th)) sage: M.frames() [Coordinate frame (R^3, (d/dr,d/dth,d/dph))] sage: e = c_spher.frame().new_frame(ch_frame, 'e') sage: e[1][:] # components of e_1 in the manifold's default frame (d/dr, d/dth, d/dth) [1, 0, 0] sage: e[2][:] [0, 1/r, 0] sage: e[3][:] [0, 0, 1/(r*sin(th))] sage: c = e.structure_coeff() ; c 3indices components w.r.t. Vector frame (R^3, (e_1,e_2,e_3)), with antisymmetry on the index positions (1, 2) sage: c[:] [[[0, 0, 0], [0, 0, 0], [0, 0, 0]], [[0, 1/r, 0], [1/r, 0, 0], [0, 0, 0]], [[0, 0, 1/r], [0, 0, cos(th)/(r*sin(th))], [1/r, cos(th)/(r*sin(th)), 0]]] sage: c[2,1,2] # C^2_{12} 1/r sage: c[3,1,3] # C^3_{13} 1/r sage: c[3,2,3] # C^3_{23} cos(th)/(r*sin(th))
 the structure coefficients \(C^k_{\ \, ij}\), as an instance of