def _del_derived(self):
r"""
Delete the derived quantities.
EXAMPLES::
sage: M = FiniteRankFreeModule(QQ, 3, name='M')
sage: e = M.basis('e')
sage: a = M.automorphism(name='a')
sage: a[e,:] = [[1,0,-1], [0,3,0], [0,0,2]]
sage: b = a.inverse()
sage: a._inverse
Automorphism a^(-1) of the 3-dimensional vector space M over the
Rational Field
sage: a._del_derived()
sage: a._inverse # has been reset to None
"""
# First delete the derived quantities pertaining to FreeModuleTensor:
FreeModuleTensor._del_derived(self)
# Then reset the inverse automorphism to None:
if self._inverse is not None:
self._inverse._inverse = None # (it was set to self)
self._inverse = None
# and delete the matrices:
self._matrices.clear()
def __init__(self, fmodule, degree, name=None, latex_name=None):
r"""
Initialize ``self``.
TESTS::
sage: from sage.tensor.modules.free_module_alt_form import FreeModuleAltForm
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = FreeModuleAltForm(M, 2, name='a')
sage: a[e,0,1] = 2
sage: TestSuite(a).run(skip="_test_category") # see below
In the above test suite, _test_category fails because a is not an
instance of a.parent().category().element_class. Actually alternating
forms must be constructed via ExtPowerFreeModule.element_class and
not by a direct call to FreeModuleAltForm::
sage: a1 = M.dual_exterior_power(2).element_class(M, 2, name='a')
sage: a1[e,0,1] = 2
sage: TestSuite(a1).run()
"""
FreeModuleTensor.__init__(self, fmodule, (0,degree), name=name,
latex_name=latex_name, antisym=range(degree),
parent=fmodule.dual_exterior_power(degree))
FreeModuleAltForm._init_derived(self) # initialization of derived
def __init__(self, fmodule, degree, name=None, latex_name=None):
r"""
Initialize ``self``.
TESTS::
sage: from sage.tensor.modules.alternating_contr_tensor import AlternatingContrTensor
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = AlternatingContrTensor(M, 2, name='a')
sage: a[e,0,1] = 2
sage: TestSuite(a).run(skip="_test_category") # see below
In the above test suite, _test_category fails because a is not an
instance of a.parent().category().element_class. Actually alternating
tensors must be constructed via ExtPowerFreeModule.element_class and
not by a direct call to AlternatingContrTensor::
sage: a1 = M.exterior_power(2).element_class(M, 2, name='a')
sage: a1[e,0,1] = 2
sage: TestSuite(a1).run()
"""
FreeModuleTensor.__init__(self,
fmodule, (degree, 0),
name=name,
latex_name=latex_name,
antisym=range(degree),
parent=fmodule.exterior_power(degree))
def __init__(self, fmodule, degree, name=None, latex_name=None):
r"""
Initialize ``self``.
TESTS::
sage: from sage.tensor.modules.free_module_alt_form import FreeModuleAltForm
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = FreeModuleAltForm(M, 2, name='a')
sage: a[e,0,1] = 2
sage: TestSuite(a).run(skip="_test_category") # see below
In the above test suite, _test_category fails because a is not an
instance of a.parent().category().element_class. Actually alternating
forms must be constructed via ExtPowerDualFreeModule.element_class and
not by a direct call to FreeModuleAltForm::
sage: a1 = M.dual_exterior_power(2).element_class(M, 2, name='a')
sage: a1[e,0,1] = 2
sage: TestSuite(a1).run()
"""
FreeModuleTensor.__init__(self, fmodule, (0,degree), name=name,
latex_name=latex_name,
antisym=range(degree),
parent=fmodule.dual_exterior_power(degree))
def _del_derived(self):
r"""
Delete the derived quantities.
EXAMPLES::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: a = M.alternating_form(2)
sage: a._del_derived()
"""
FreeModuleTensor._del_derived(self)
def _del_derived(self):
r"""
Delete the derived quantities.
EXAMPLES::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: a = M.alternating_form(2)
sage: a._del_derived()
"""
FreeModuleTensor._del_derived(self)
def __init__(self, fmodule, name=None, latex_name=None, is_identity=False):
r"""
TESTS::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: from sage.tensor.modules.free_module_automorphism import FreeModuleAutomorphism
sage: a = FreeModuleAutomorphism(M, name='a')
sage: a[e,:] = [[-1,0,0],[0,1,2],[0,1,3]]
sage: TestSuite(a).run(skip="_test_category") # see below
In the above test suite, _test_category fails because a is not an
instance of a.parent().category().element_class. Actually automorphism
must be constructed via FreeModuleLinearGroup.element_class and
not by a direct call to FreeModuleAutomorphism::
sage: a = M.general_linear_group().element_class(M, name='a')
sage: a[e,:] = [[-1,0,0],[0,1,2],[0,1,3]]
sage: TestSuite(a).run()
Test suite on the identity map::
sage: id = M.general_linear_group().one()
sage: TestSuite(id).run()
Test suite on the automorphism obtained as GL.an_element()::
sage: b = M.general_linear_group().an_element()
sage: TestSuite(b).run()
"""
if is_identity:
if name is None:
name = 'Id'
if latex_name is None:
if name == 'Id':
latex_name = r'\mathrm{Id}'
else:
latex_name = name
FreeModuleTensor.__init__(self,
fmodule, (1, 1),
name=name,
latex_name=latex_name,
parent=fmodule.general_linear_group())
# MultiplicativeGroupElement attributes:
# - none
# Local attributes:
self._is_identity = is_identity
self._inverse = None # inverse automorphism not set yet
self._matrices = {}
def __init__(self, fmodule, name=None, latex_name=None, is_identity=False):
r"""
TESTS::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: from sage.tensor.modules.free_module_automorphism import FreeModuleAutomorphism
sage: a = FreeModuleAutomorphism(M, name='a')
sage: a[e,:] = [[-1,0,0],[0,1,2],[0,1,3]]
sage: TestSuite(a).run(skip="_test_category") # see below
In the above test suite, _test_category fails because a is not an
instance of a.parent().category().element_class. Actually automorphism
must be constructed via FreeModuleLinearGroup.element_class and
not by a direct call to FreeModuleAutomorphism::
sage: a = M.general_linear_group().element_class(M, name='a')
sage: a[e,:] = [[-1,0,0],[0,1,2],[0,1,3]]
sage: TestSuite(a).run()
Test suite on the identity map::
sage: id = M.general_linear_group().one()
sage: TestSuite(id).run()
Test suite on the automorphism obtained as GL.an_element()::
sage: b = M.general_linear_group().an_element()
sage: TestSuite(b).run()
"""
if is_identity:
if name is None:
name = 'Id'
if latex_name is None:
if name == 'Id':
latex_name = r'\mathrm{Id}'
else:
latex_name = name
FreeModuleTensor.__init__(self, fmodule, (1,1), name=name,
latex_name=latex_name,
parent=fmodule.general_linear_group())
# MultiplicativeGroupElement attributes:
# - none
# Local attributes:
self._is_identity = is_identity
self._inverse = None # inverse automorphism not set yet
self._matrices = {}
def __mul__(self, other):
r"""
Redefinition of
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.__mul__`
so that * dispatches either to automorphism composition or to the
tensor product.
EXAMPLES:
Automorphism composition::
sage: M = FiniteRankFreeModule(ZZ, 2, name='M')
sage: e = M.basis('e')
sage: a = M.automorphism([[1,2],[1,3]])
sage: b = M.automorphism([[3,4],[5,7]])
sage: s = a*b ; s
Automorphism of the Rank-2 free module M over the Integer Ring
sage: s.matrix()
[13 18]
[18 25]
sage: s.matrix() == a.matrix() * b.matrix()
True
sage: s(e[0]) == a(b(e[0]))
True
sage: s(e[1]) == a(b(e[1]))
True
sage: s.display()
13 e_0*e^0 + 18 e_0*e^1 + 18 e_1*e^0 + 25 e_1*e^1
Tensor product::
sage: c = M.tensor((1,1)) ; c
Type-(1,1) tensor on the Rank-2 free module M over the Integer Ring
sage: c[:] = [[3,4],[5,7]]
sage: c[:] == b[:] # c and b have the same components
True
sage: s = a*c ; s
Type-(2,2) tensor on the Rank-2 free module M over the Integer Ring
sage: s.display()
3 e_0*e_0*e^0*e^0 + 4 e_0*e_0*e^0*e^1 + 6 e_0*e_0*e^1*e^0
+ 8 e_0*e_0*e^1*e^1 + 5 e_0*e_1*e^0*e^0 + 7 e_0*e_1*e^0*e^1
+ 10 e_0*e_1*e^1*e^0 + 14 e_0*e_1*e^1*e^1 + 3 e_1*e_0*e^0*e^0
+ 4 e_1*e_0*e^0*e^1 + 9 e_1*e_0*e^1*e^0 + 12 e_1*e_0*e^1*e^1
+ 5 e_1*e_1*e^0*e^0 + 7 e_1*e_1*e^0*e^1 + 15 e_1*e_1*e^1*e^0
+ 21 e_1*e_1*e^1*e^1
"""
if isinstance(other, FreeModuleAutomorphism):
return self._mul_(other) # general linear group law
else:
return FreeModuleTensor.__mul__(self, other) # tensor product
def __mul__(self, other):
r"""
Redefinition of
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.__mul__`
so that * dispatches either to automorphism composition or to the
tensor product.
EXAMPLES:
Automorphism composition::
sage: M = FiniteRankFreeModule(ZZ, 2, name='M')
sage: e = M.basis('e')
sage: a = M.automorphism([[1,2],[1,3]])
sage: b = M.automorphism([[3,4],[5,7]])
sage: s = a*b ; s
Automorphism of the Rank-2 free module M over the Integer Ring
sage: s.matrix()
[13 18]
[18 25]
sage: s.matrix() == a.matrix() * b.matrix()
True
sage: s(e[0]) == a(b(e[0]))
True
sage: s(e[1]) == a(b(e[1]))
True
sage: s.display()
13 e_0*e^0 + 18 e_0*e^1 + 18 e_1*e^0 + 25 e_1*e^1
Tensor product::
sage: c = M.tensor((1,1)) ; c
Type-(1,1) tensor on the Rank-2 free module M over the Integer Ring
sage: c[:] = [[3,4],[5,7]]
sage: c[:] == b[:] # c and b have the same components
True
sage: s = a*c ; s
Type-(2,2) tensor on the Rank-2 free module M over the Integer Ring
sage: s.display()
3 e_0*e_0*e^0*e^0 + 4 e_0*e_0*e^0*e^1 + 6 e_0*e_0*e^1*e^0
+ 8 e_0*e_0*e^1*e^1 + 5 e_0*e_1*e^0*e^0 + 7 e_0*e_1*e^0*e^1
+ 10 e_0*e_1*e^1*e^0 + 14 e_0*e_1*e^1*e^1 + 3 e_1*e_0*e^0*e^0
+ 4 e_1*e_0*e^0*e^1 + 9 e_1*e_0*e^1*e^0 + 12 e_1*e_0*e^1*e^1
+ 5 e_1*e_1*e^0*e^0 + 7 e_1*e_1*e^0*e^1 + 15 e_1*e_1*e^1*e^0
+ 21 e_1*e_1*e^1*e^1
"""
if isinstance(other, FreeModuleAutomorphism):
return self._mul_(other) # general linear group law
else:
return FreeModuleTensor.__mul__(self, other) # tensor product
def _new_comp(self, basis):
r"""
Create some (uninitialized) components of ``self`` in a given basis.
INPUT:
- ``basis`` -- basis of the free module on which ``self`` is defined
OUTPUT:
- an instance of :class:`~sage.tensor.modules.comp.Components` or,
if ``self`` is the identity, of the subclass
:class:`~sage.tensor.modules.comp.KroneckerDelta`
EXAMPLES::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = M.automorphism()
sage: a._new_comp(e)
2-indices components w.r.t. Basis (e_0,e_1,e_2) on the Rank-3 free
module M over the Integer Ring
sage: id = M.identity_map()
sage: id._new_comp(e)
Kronecker delta of size 3x3
sage: type(id._new_comp(e))
<class 'sage.tensor.modules.comp.KroneckerDelta'>
"""
from .comp import KroneckerDelta
if self._is_identity:
fmodule = self._fmodule
return KroneckerDelta(
fmodule._ring, basis, start_index=fmodule._sindex, output_formatter=fmodule._output_formatter
)
return FreeModuleTensor._new_comp(self, basis)
def _new_comp(self, basis):
r"""
Create some (uninitialized) components of ``self`` in a given basis.
INPUT:
- ``basis`` -- basis of the free module on which ``self`` is defined
OUTPUT:
- an instance of :class:`~sage.tensor.modules.comp.Components` or,
if ``self`` is the identity, of the subclass
:class:`~sage.tensor.modules.comp.KroneckerDelta`
EXAMPLES::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = M.automorphism()
sage: a._new_comp(e)
2-indices components w.r.t. Basis (e_0,e_1,e_2) on the Rank-3 free
module M over the Integer Ring
sage: id = M.identity_map()
sage: id._new_comp(e)
Kronecker delta of size 3x3
sage: type(id._new_comp(e))
<class 'sage.tensor.modules.comp.KroneckerDelta'>
"""
from comp import KroneckerDelta
if self._is_identity:
fmodule = self._fmodule
return KroneckerDelta(fmodule._ring,
basis,
start_index=fmodule._sindex,
output_formatter=fmodule._output_formatter)
return FreeModuleTensor._new_comp(self, basis)
def __call__(self, *arg):
r"""
Redefinition of :meth:`FreeModuleTensor.__call__` to allow for a single
argument (module element).
EXAMPLES:
Call with a single argument: return a module element::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M', start_index=1)
sage: e = M.basis('e')
sage: a = M.automorphism([[-1,0,0],[0,1,2],[0,1,3]], name='a')
sage: v = M([2,1,4], name='v')
sage: s = a.__call__(v) ; s
Element a(v) of the Rank-3 free module M over the Integer Ring
sage: s.display()
a(v) = -2 e_1 + 9 e_2 + 13 e_3
sage: s == a(v)
True
sage: s == a.contract(v)
True
Call with two arguments (:class:`FreeModuleTensor` behaviour): return a
scalar::
sage: b = M.linear_form(name='b')
sage: b[:] = 7, 0, 2
sage: a.__call__(b,v)
12
sage: a(b,v) == a.__call__(b,v)
True
sage: a(b,v) == s(b)
True
Identity map with a single argument: return a module element::
sage: id = M.identity_map()
sage: s = id.__call__(v) ; s
Element v of the Rank-3 free module M over the Integer Ring
sage: s == v
True
sage: s == id(v)
True
sage: s == id.contract(v)
True
Identity map with two arguments (:class:`FreeModuleTensor` behaviour):
return a scalar::
sage: id.__call__(b,v)
22
sage: id(b,v) == id.__call__(b,v)
True
sage: id(b,v) == b(v)
True
"""
from .free_module_tensor import FiniteRankFreeModuleElement
if len(arg) > 1:
# The automorphism acting as a type-(1,1) tensor on a pair
# (linear form, module element), returning a scalar:
if self._is_identity:
if len(arg) != 2:
raise TypeError("wrong number of arguments")
linform = arg[0]
if linform._tensor_type != (0,1):
raise TypeError("the first argument must be a linear form")
vector = arg[1]
if not isinstance(vector, FiniteRankFreeModuleElement):
raise TypeError("the second argument must be a module" +
" element")
return linform(vector)
else: # self is not the identity automorphism:
return FreeModuleTensor.__call__(self, *arg)
# The automorphism acting as such, on a module element, returning a
# module element:
vector = arg[0]
if not isinstance(vector, FiniteRankFreeModuleElement):
raise TypeError("the argument must be an element of a free module")
if self._is_identity:
return vector
basis = self.common_basis(vector)
t = self._components[basis]
v = vector._components[basis]
fmodule = self._fmodule
result = vector._new_instance()
for i in fmodule.irange():
res = 0
for j in fmodule.irange():
res += t[[i,j]]*v[[j]]
result.set_comp(basis)[i] = res
# Name of the output:
result._name = None
if self._name is not None and vector._name is not None:
result._name = self._name + "(" + vector._name + ")"
# LaTeX symbol for the output:
result._latex_name = None
if self._latex_name is not None and vector._latex_name is not None:
result._latex_name = self._latex_name + r"\left(" + \
vector._latex_name + r"\right)"
return result
def add_comp(self, basis=None):
r"""
Return the components of ``self`` w.r.t. a given module basis for
assignment, keeping the components w.r.t. other bases.
To delete the components w.r.t. other bases, use the method
:meth:`set_comp` instead.
INPUT:
- ``basis`` -- (default: ``None``) basis in which the components are
defined; if none is provided, the components are assumed to refer to
the module's default basis
.. WARNING::
If the automorphism has already components in other bases, it
is the user's responsability to make sure that the components
to be added are consistent with them.
OUTPUT:
- components in the given basis, as an instance of the
class :class:`~sage.tensor.modules.comp.Components`;
if such components did not exist previously, they are created
EXAMPLES:
Adding components to an automorphism of a rank-3 free
`\ZZ`-module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = M.automorphism(name='a')
sage: a[e,:] = [[1,0,0],[0,-1,2],[0,1,-3]]
sage: f = M.basis('f', from_family=(-e[0], 3*e[1]+4*e[2],
....: 5*e[1]+7*e[2])) ; f
Basis (f_0,f_1,f_2) on the Rank-3 free module M over the Integer
Ring
sage: a.add_comp(f)[:] = [[1,0,0], [0, 80, 143], [0, -47, -84]]
The components in basis ``e`` have been kept::
sage: a._components # random (dictionary output)
{Basis (e_0,e_1,e_2) on the Rank-3 free module M over the Integer
Ring: 2-indices components w.r.t. Basis (e_0,e_1,e_2) on the
Rank-3 free module M over the Integer Ring,
Basis (f_0,f_1,f_2) on the Rank-3 free module M over the Integer
Ring: 2-indices components w.r.t. Basis (f_0,f_1,f_2) on the
Rank-3 free module M over the Integer Ring}
For the identity map, it is not permitted to invoke :meth:`add_comp`::
sage: id = M.identity_map()
sage: id.add_comp(e)
Traceback (most recent call last):
...
TypeError: the components of the identity map cannot be changed
Indeed, the components are automatically set by a call to
:meth:`comp`::
sage: id.comp(e)
Kronecker delta of size 3x3
sage: id.comp(f)
Kronecker delta of size 3x3
"""
if self._is_identity:
raise TypeError("the components of the identity map cannot be " +
"changed")
else:
return FreeModuleTensor.add_comp(self, basis=basis)
def set_comp(self, basis=None):
r"""
Return the components of ``self`` w.r.t. a given module basis for
assignment.
The components with respect to other bases are deleted, in order to
avoid any inconsistency. To keep them, use the method :meth:`add_comp`
instead.
INPUT:
- ``basis`` -- (default: ``None``) basis in which the components are
defined; if none is provided, the components are assumed to refer to
the module's default basis
OUTPUT:
- components in the given basis, as an instance of the
class :class:`~sage.tensor.modules.comp.Components`; if such
components did not exist previously, they are created.
EXAMPLES:
Setting the components of an automorphism of a rank-3 free
`\ZZ`-module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = M.automorphism(name='a')
sage: a.set_comp(e)
2-indices components w.r.t. Basis (e_0,e_1,e_2) on the Rank-3 free
module M over the Integer Ring
sage: a.set_comp(e)[:] = [[1,0,0],[0,1,2],[0,1,3]]
sage: a.matrix(e)
[1 0 0]
[0 1 2]
[0 1 3]
Since ``e`` is the module's default basis, one has::
sage: a.set_comp() is a.set_comp(e)
True
The method :meth:`set_comp` can be used to modify a single component::
sage: a.set_comp(e)[0,0] = -1
sage: a.matrix(e)
[-1 0 0]
[ 0 1 2]
[ 0 1 3]
A short cut to :meth:`set_comp` is the bracket operator, with the basis
as first argument::
sage: a[e,:] = [[1,0,0],[0,-1,2],[0,1,-3]]
sage: a.matrix(e)
[ 1 0 0]
[ 0 -1 2]
[ 0 1 -3]
sage: a[e,0,0] = -1
sage: a.matrix(e)
[-1 0 0]
[ 0 -1 2]
[ 0 1 -3]
The call to :meth:`set_comp` erases the components previously defined
in other bases; to keep them, use the method :meth:`add_comp` instead::
sage: f = M.basis('f', from_family=(-e[0], 3*e[1]+4*e[2],
....: 5*e[1]+7*e[2])) ; f
Basis (f_0,f_1,f_2) on the Rank-3 free module M over the Integer
Ring
sage: a._components
{Basis (e_0,e_1,e_2) on the Rank-3 free module M over the Integer
Ring: 2-indices components w.r.t. Basis (e_0,e_1,e_2) on the
Rank-3 free module M over the Integer Ring}
sage: a.set_comp(f)[:] = [[-1,0,0], [0,1,0], [0,0,-1]]
The components w.r.t. basis ``e`` have been erased::
sage: a._components
{Basis (f_0,f_1,f_2) on the Rank-3 free module M over the Integer
Ring: 2-indices components w.r.t. Basis (f_0,f_1,f_2) on the
Rank-3 free module M over the Integer Ring}
Of course, they can be computed from those in basis ``f`` by means of
a change-of-basis formula, via the method :meth:`comp` or
:meth:`matrix`::
sage: a.matrix(e)
[ -1 0 0]
[ 0 41 -30]
[ 0 56 -41]
For the identity map, it is not permitted to set components::
sage: id = M.identity_map()
sage: id.set_comp(e)
Traceback (most recent call last):
...
TypeError: the components of the identity map cannot be changed
Indeed, the components are automatically set by a call to
:meth:`comp`::
sage: id.comp(e)
Kronecker delta of size 3x3
sage: id.comp(f)
Kronecker delta of size 3x3
"""
if self._is_identity:
raise TypeError("the components of the identity map cannot be " +
"changed")
else:
return FreeModuleTensor.set_comp(self, basis=basis)
def components(self, basis=None, from_basis=None):
r"""
Return the components of ``self`` w.r.t to a given module basis.
If the components are not known already, they are computed by the
tensor change-of-basis formula from components in another basis.
INPUT:
- ``basis`` -- (default: ``None``) basis in which the components are
required; if none is provided, the components are assumed to refer
to the module's default basis
- ``from_basis`` -- (default: ``None``) basis from which the
required components are computed, via the tensor change-of-basis
formula, if they are not known already in the basis ``basis``;
if none, a basis from which both the components and a change-of-basis
to ``basis`` are known is selected.
OUTPUT:
- components in the basis ``basis``, as an instance of the
class :class:`~sage.tensor.modules.comp.Components`,
or, for the identity automorphism, of the subclass
:class:`~sage.tensor.modules.comp.KroneckerDelta`
EXAMPLES:
Components of an automorphism on a rank-3 free `\ZZ`-module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M', start_index=1)
sage: e = M.basis('e')
sage: a = M.automorphism([[-1,0,0],[0,1,2],[0,1,3]], name='a')
sage: a.components(e)
2-indices components w.r.t. Basis (e_1,e_2,e_3) on the Rank-3 free
module M over the Integer Ring
sage: a.components(e)[:]
[-1 0 0]
[ 0 1 2]
[ 0 1 3]
Since e is the module's default basis, it can be omitted::
sage: a.components() is a.components(e)
True
A shortcut is ``a.comp()``::
sage: a.comp() is a.components()
True
sage: a.comp(e) is a.components()
True
Components in another basis::
sage: f1 = -e[2]
sage: f2 = 4*e[1] + 3*e[3]
sage: f3 = 7*e[1] + 5*e[3]
sage: f = M.basis('f', from_family=(f1,f2,f3))
sage: a.components(f)
2-indices components w.r.t. Basis (f_1,f_2,f_3) on the Rank-3 free
module M over the Integer Ring
sage: a.components(f)[:]
[ 1 -6 -10]
[ -7 83 140]
[ 4 -48 -81]
Some check of the above matrix::
sage: a(f[1]).display(f)
a(f_1) = f_1 - 7 f_2 + 4 f_3
sage: a(f[2]).display(f)
a(f_2) = -6 f_1 + 83 f_2 - 48 f_3
sage: a(f[3]).display(f)
a(f_3) = -10 f_1 + 140 f_2 - 81 f_3
Components of the identity map::
sage: id = M.identity_map()
sage: id.components(e)
Kronecker delta of size 3x3
sage: id.components(e)[:]
[1 0 0]
[0 1 0]
[0 0 1]
sage: id.components(f)
Kronecker delta of size 3x3
sage: id.components(f)[:]
[1 0 0]
[0 1 0]
[0 0 1]
"""
if self._is_identity:
if basis is None:
basis = self._fmodule._def_basis
if basis not in self._components:
self._components[basis] = self._new_comp(basis)
return self._components[basis]
else:
return FreeModuleTensor.components(self, basis=basis,
from_basis=from_basis)