def __invert__(self):
r"""
Return the inverse automorphism.
OUTPUT:
- instance of :class:`FreeModuleAutomorphism` representing the
automorphism that is the inverse of ``self``.
EXAMPLES:
Inverse of an automorphism of a rank-3 free 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: a.inverse()
Automorphism a^(-1) of the Rank-3 free module M over the Integer
Ring
sage: a.inverse().parent()
General linear group of the Rank-3 free module M over the Integer
Ring
Check that ``a.inverse()`` is indeed the inverse automorphism::
sage: a.inverse() * a
Identity map of the Rank-3 free module M over the Integer Ring
sage: a * a.inverse()
Identity map of the Rank-3 free module M over the Integer Ring
sage: a.inverse().inverse() == a
True
Another check is::
sage: a.inverse().matrix(e)
[ 1 0 0]
[ 0 -3 -2]
[ 0 -1 -1]
sage: a.inverse().matrix(e) == (a.matrix(e))^(-1)
True
The inverse is cached (as long as ``a`` is not modified)::
sage: a.inverse() is a.inverse()
True
If ``a`` is modified, the inverse is automatically recomputed::
sage: a[0,0] = -1
sage: a.matrix(e)
[-1 0 0]
[ 0 -1 2]
[ 0 1 -3]
sage: a.inverse().matrix(e) # compare with above
[-1 0 0]
[ 0 -3 -2]
[ 0 -1 -1]
Shortcuts for :meth:`inverse` are the operator ``~`` and the exponent
``-1``::
sage: ~a is a.inverse()
True
sage: (a)^(-1) is a.inverse()
True
The inverse of the identity map is of course itself::
sage: id = M.identity_map()
sage: id.inverse() is id
True
and we have::
sage: a*(a)^(-1) == id
True
sage: (a)^(-1)*a == id
True
If the name could cause some confusion, a bracket is added around the
element before taking the inverse::
sage: c = M.automorphism(name='a^(-1)*b')
sage: c[e,:] = [[1,0,0],[0,-1,1],[0,2,-1]]
sage: c.inverse()
Automorphism (a^(-1)*b)^(-1) of the Rank-3 free module M over the
Integer Ring
"""
from .comp import Components
if self._is_identity:
return self
if self._inverse is None:
from sage.tensor.modules.format_utilities import is_atomic
if self._name is None:
inv_name = None
else:
if is_atomic(self._name, ['*']):
inv_name = self._name + '^(-1)'
else:
inv_name = '(' + self._name + ')^(-1)'
if self._latex_name is None:
inv_latex_name = None
else:
if is_atomic(self._latex_name, ['\\circ', '\\otimes']):
inv_latex_name = self._latex_name + r'^{-1}'
else:
inv_latex_name = r'\left(' + self._latex_name + \
r'\right)^{-1}'
fmodule = self._fmodule
si = fmodule._sindex
nsi = fmodule._rank + si
self._inverse = self.__class__(fmodule, inv_name, inv_latex_name)
for basis in self._components:
try:
mat = self.matrix(basis)
except (KeyError, ValueError):
continue
mat_inv = mat.inverse()
cinv = Components(fmodule._ring, basis, 2, start_index=si,
output_formatter=fmodule._output_formatter)
for i in range(si, nsi):
for j in range(si, nsi):
cinv[i, j] = mat_inv[i-si,j-si]
self._inverse._components[basis] = cinv
self._inverse._inverse = self
return self._inverse
def wedge(self, other):
r"""
Exterior product of ``self`` with the alternating form ``other``.
INPUT:
- ``other`` -- an alternating form
OUTPUT:
- instance of :class:`FreeModuleAltForm` representing the exterior
product ``self/\other``
EXAMPLES:
Exterior product of two linear forms::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = M.linear_form('A')
sage: a[:] = [1,-3,4]
sage: b = M.linear_form('B')
sage: b[:] = [2,-1,2]
sage: c = a.wedge(b) ; c
Alternating form A/\B of degree 2 on the Rank-3 free module M
over the Integer Ring
sage: c.display()
A/\B = 5 e^0/\e^1 - 6 e^0/\e^2 - 2 e^1/\e^2
sage: latex(c)
A\wedge B
sage: latex(c.display())
A\wedge B = 5 e^0\wedge e^1 -6 e^0\wedge e^2 -2 e^1\wedge e^2
Test of the computation::
sage: a.wedge(b) == a*b - b*a
True
Exterior product of a linear form and an alternating form of degree 2::
sage: d = M.linear_form('D')
sage: d[:] = [-1,2,4]
sage: s = d.wedge(c) ; s
Alternating form D/\A/\B of degree 3 on the Rank-3 free module M
over the Integer Ring
sage: s.display()
D/\A/\B = 34 e^0/\e^1/\e^2
Test of the computation::
sage: s[0,1,2] == d[0]*c[1,2] + d[1]*c[2,0] + d[2]*c[0,1]
True
Let us check that the exterior product is associative::
sage: d.wedge(a.wedge(b)) == (d.wedge(a)).wedge(b)
True
and that it is graded anticommutative::
sage: a.wedge(b) == - b.wedge(a)
True
sage: d.wedge(c) == c.wedge(d)
True
"""
from .format_utilities import is_atomic
if not isinstance(other, FreeModuleAltForm):
raise TypeError("the second argument for the exterior product " +
"must be an alternating form")
if other._tensor_rank == 0:
return other*self
if self._tensor_rank == 0:
return self*other
fmodule = self._fmodule
basis = self.common_basis(other)
if basis is None:
raise ValueError("no common basis for the exterior product")
rank_r = self._tensor_rank + other._tensor_rank
cmp_s = self._components[basis]
cmp_o = other._components[basis]
cmp_r = CompFullyAntiSym(fmodule._ring, basis, rank_r,
start_index=fmodule._sindex,
output_formatter=fmodule._output_formatter)
for ind_s, val_s in six.iteritems(cmp_s._comp):
for ind_o, val_o in six.iteritems(cmp_o._comp):
ind_r = ind_s + ind_o
if len(ind_r) == len(set(ind_r)): # all indices are different
cmp_r[[ind_r]] += val_s * val_o
result = fmodule.alternating_form(rank_r)
result._components[basis] = cmp_r
if self._name is not None and other._name is not None:
sname = self._name
oname = other._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
result._name = sname + '/\\' + oname
if self._latex_name is not None and other._latex_name is not None:
slname = self._latex_name
olname = other._latex_name
if not is_atomic(slname):
slname = '(' + slname + ')'
if not is_atomic(olname):
olname = '(' + olname + ')'
result._latex_name = slname + r'\wedge ' + olname
return result
def wedge(self, other):
r"""
Exterior product with another differential form.
INPUT:
- ``other`` -- another differential form (on the same manifold)
OUTPUT:
- a :class:`DiffForm` of the exterior product ``self/\other``
EXAMPLES:
Exterior product of two 1-forms on the 2-sphere::
sage: M = Manifold(2, 'S^2', start_index=1) # the 2-dimensional sphere S^2
sage: U = M.open_subset('U') ; V = M.open_subset('V')
sage: M.declare_union(U,V) # S^2 is the union of U and V
sage: c_xy.<x,y> = U.chart() ; c_uv.<u,v> = V.chart() # stereographic coord. (North and South)
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: W = U.intersection(V) # The complement of the two poles
sage: e_xy = c_xy.frame() ; e_uv = c_uv.frame()
sage: a = M.diff_form(1, name='a')
sage: a[e_xy,:] = y, x
sage: a.add_comp_by_continuation(e_uv, W, c_uv)
sage: b = M.diff_form(1, name='b')
sage: b[e_xy,:] = x^2 + y^2, y
sage: b.add_comp_by_continuation(e_uv, W, c_uv)
sage: c = a.wedge(b); c
2-form a/\b on the 2-dimensional differentiable manifold S^2
sage: c.display(e_xy)
a/\b = (-x^3 - (x - 1)*y^2) dx/\dy
sage: c.display(e_uv)
a/\b = -(v^2 - u)/(u^8 + 4*u^6*v^2 + 6*u^4*v^4 + 4*u^2*v^6 + v^8) du/\dv
"""
from sage.tensor.modules.free_module_alt_form import FreeModuleAltForm
from sage.tensor.modules.format_utilities import is_atomic
if self._domain.is_subset(other._domain):
if not self._ambient_domain.is_subset(other._ambient_domain):
raise ValueError(
"incompatible ambient domains for exterior product")
elif other._domain.is_subset(self._domain):
if not other._ambient_domain.is_subset(self._ambient_domain):
raise ValueError(
"incompatible ambient domains for exterior product")
dom_resu = self._domain.intersection(other._domain)
ambient_dom_resu = self._ambient_domain.intersection(
other._ambient_domain)
self_r = self.restrict(dom_resu)
other_r = other.restrict(dom_resu)
if ambient_dom_resu.is_manifestly_parallelizable():
# call of the FreeModuleAltForm version:
return FreeModuleAltForm.wedge(self_r, other_r)
# otherwise, the result is created here:
if self._name is not None and other._name is not None:
sname = self._name
oname = other._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
resu_name = sname + '/\\' + oname
if self._latex_name is not None and other._latex_name is not None:
slname = self._latex_name
olname = other._latex_name
if not is_atomic(slname):
slname = '(' + slname + ')'
if not is_atomic(olname):
olname = '(' + olname + ')'
resu_latex_name = slname + r'\wedge ' + olname
dest_map = self._vmodule._dest_map
dest_map_resu = dest_map.restrict(dom_resu,
subcodomain=ambient_dom_resu)
vmodule = dom_resu.vector_field_module(dest_map=dest_map_resu)
resu_degree = self._tensor_rank + other._tensor_rank
resu = vmodule.alternating_form(resu_degree,
name=resu_name,
latex_name=resu_latex_name)
for dom in self_r._restrictions:
if dom in other_r._restrictions:
resu._restrictions[dom] = self_r._restrictions[dom].wedge(
other_r._restrictions[dom])
return resu
def interior_product(self, form):
r"""
Interior product with an alternating form.
If ``self`` is an alternating contravariant tensor `A` of degree `p`
and `B` is an alternating form of degree `q\geq p` on the same free
module, the interior product of `A` by `B` is the alternating form
`\iota_A B` of degree `q-p` defined by
.. MATH::
(\iota_A B)_{i_1\ldots i_{q-p}} = A^{k_1\ldots k_p}
B_{k_1\ldots k_p i_1\ldots i_{q-p}}
.. NOTE::
``A.interior_product(B)`` yields the same result as
``A.contract(0,..., p-1, B, 0,..., p-1)`` (cf.
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.contract`),
but ``interior_product`` is more efficient, the alternating
character of `A` being not used to reduce the computation in
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.contract`
INPUT:
- ``form`` -- alternating form `B` (instance of
:class:`~sage.tensor.modules.free_module_alt_form.FreeModuleAltForm`);
the degree of `B` must be at least equal to the degree of ``self``
OUTPUT:
- element of the base ring (case `p=q`) or
:class:`~sage.tensor.modules.free_module_alt_form.FreeModuleAltForm`
(case `p<q`) representing the interior product `\iota_A B`, where `A`
is ``self``
.. SEEALSO::
:meth:`~sage.tensor.modules.free_module_alt_form.FreeModuleAltForm.interior_product`
for the interior product of an alternating form by an alternating
contravariant tensor
EXAMPLES:
Let us consider a rank-4 free module::
sage: M = FiniteRankFreeModule(ZZ, 4, name='M', start_index=1)
sage: e = M.basis('e')
and various interior products on it, starting with a module element
(``p=1``) and a linear form (``q=1``)::
sage: a = M([-2,1,2,3], basis=e, name='A')
sage: b = M.linear_form(name='B')
sage: b[:] = [2, 0, -3, 4]
sage: c = a.interior_product(b); c
2
sage: c == a.contract(b)
True
Case ``p=1`` and ``q=3``::
sage: b = M.alternating_form(3, name='B')
sage: b[1,2,3], b[1,2,4], b[1,3,4], b[2,3,4] = 3, -1, 2, 5
sage: c = a.interior_product(b); c
Alternating form i_A B of degree 2 on the Rank-4 free module M over the Integer Ring
sage: c.display()
i_A B = 3 e^1/\e^2 + 3 e^1/\e^3 - 3 e^1/\e^4 + 9 e^2/\e^3 - 8 e^2/\e^4 + e^3/\e^4
sage: latex(c)
\iota_{A} B
sage: c == a.contract(b)
True
Case ``p=2`` and ``q=3``::
sage: a = M.alternating_contravariant_tensor(2, name='A')
sage: a[1,2], a[1,3], a[1,4] = 2, -5, 3
sage: a[2,3], a[2,4], a[3,4] = -1, 4, 2
sage: c = a.interior_product(b); c
Linear form i_A B on the Rank-4 free module M over the Integer Ring
sage: c.display()
i_A B = -6 e^1 + 56 e^2 - 40 e^3 - 34 e^4
sage: c == a.contract(0, 1, b, 0, 1) # contraction on all indices of a
True
Case ``p=2`` and ``q=4``::
sage: b = M.alternating_form(4, name='B')
sage: b[1,2,3,4] = 5
sage: c = a.interior_product(b); c
Alternating form i_A B of degree 2 on the Rank-4 free module M over the Integer Ring
sage: c.display()
i_A B = 20 e^1/\e^2 - 40 e^1/\e^3 - 10 e^1/\e^4 + 30 e^2/\e^3 + 50 e^2/\e^4 + 20 e^3/\e^4
sage: c == a.contract(0, 1, b, 0, 1)
True
Case ``p=2`` and ``q=2``::
sage: b = M.alternating_form(2)
sage: b[1,2], b[1,3], b[1,4] = 6, 0, -2
sage: b[2,3], b[2,4], b[3,4] = 2, 3, 4
sage: c = a.interior_product(b); c
48
sage: c == a.contract(0, 1, b, 0, 1)
True
Case ``p=3`` and ``q=3``::
sage: a = M.alternating_contravariant_tensor(3, name='A')
sage: a[1,2,3], a[1,2,4], a[1,3,4], a[2,3,4] = -3, 2, 8, -5
sage: b = M.alternating_form(3, name='B')
sage: b[1,2,3], b[1,2,4], b[1,3,4], b[2,3,4] = 3, -1, 2, 5
sage: c = a.interior_product(b); c
-120
sage: c == a.contract(0, 1, 2, b, 0, 1, 2)
True
Case ``p=3`` and ``q=4``::
sage: b = M.alternating_form(4, name='B')
sage: b[1,2,3,4] = 5
sage: c = a.interior_product(b); c
Linear form i_A B on the Rank-4 free module M over the Integer Ring
sage: c.display()
i_A B = 150 e^1 + 240 e^2 - 60 e^3 - 90 e^4
sage: c == a.contract(0, 1, 2, b, 0, 1, 2)
True
Case ``p=4`` and ``q=4``::
sage: a = M.alternating_contravariant_tensor(4, name='A')
sage: a[1,2,3,4] = -2
sage: c = a.interior_product(b); c
-240
sage: c == a.contract(0, 1, 2, 3, b, 0, 1, 2, 3)
True
"""
from .format_utilities import is_atomic
from .free_module_alt_form import FreeModuleAltForm
if not isinstance(form, FreeModuleAltForm):
raise TypeError("{} is not an alternating form".format(form))
p_res = form._tensor_rank - self._tensor_rank # degree of the result
if self._tensor_rank == 1:
# Case p = 1:
res = self.contract(form) # contract() deals efficiently with
# the antisymmetry for p = 1
else:
# Case p > 1:
if form._fmodule != self._fmodule:
raise ValueError(
"{} is not defined on the same ".format(form) +
"module as the {}".format(self))
if form._tensor_rank < self._tensor_rank:
raise ValueError(
"the degree of the {} is lower ".format(form) +
"than that of the {}".format(self))
# Interior product at the component level:
basis = self.common_basis(form)
if basis is None:
raise ValueError("no common basis for the interior product")
comp = self._components[basis].interior_product(
form._components[basis])
if p_res == 0:
res = comp # result is a scalar
else:
res = self._fmodule.tensor_from_comp((0, p_res), comp)
# Name of the result
res_name = None
if self._name is not None and form._name is not None:
sname = self._name
oname = form._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
res_name = 'i_' + sname + ' ' + oname
res_latex_name = None
if self._latex_name is not None and form._latex_name is not None:
slname = self._latex_name
olname = form._latex_name
if not is_atomic(olname):
olname = r'\left(' + olname + r'\right)'
res_latex_name = r'\iota_{' + slname + '} ' + olname
if p_res == 0:
if res_name:
try: # there is no guarantee that base ring elements have
# set_name
res.set_name(res_name, latex_name=res_latex_name)
except (AttributeError, TypeError):
pass
else:
res.set_name(res_name, latex_name=res_latex_name)
return res
def display(self, basis=None, format_spec=None):
r"""
Display the alternating form ``self`` in terms of its expansion w.r.t.
a given module basis.
The expansion is actually performed onto exterior products of elements
of the cobasis (dual basis) associated with ``basis`` (see examples
below). The output is either text-formatted (console mode) or
LaTeX-formatted (notebook mode).
INPUT:
- ``basis`` -- (default: ``None``) basis of the free module with
respect to which the alternating form is expanded; if none is
provided, the module's default basis is assumed
- ``format_spec`` -- (default: ``None``) format specification passed
to ``self._fmodule._output_formatter`` to format the output
EXAMPLES:
Display of an alternating form of degree 1 (linear form) on a rank-3
free module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: e.dual_basis()
Dual basis (e^0,e^1,e^2) on the Rank-3 free module M over the Integer Ring
sage: a = M.linear_form('a', latex_name=r'\alpha')
sage: a[:] = [1,-3,4]
sage: a.display(e)
a = e^0 - 3 e^1 + 4 e^2
sage: a.display() # a shortcut since e is M's default basis
a = e^0 - 3 e^1 + 4 e^2
sage: latex(a.display()) # display in the notebook
\alpha = e^0 -3 e^1 + 4 e^2
A shortcut is ``disp()``::
sage: a.disp()
a = e^0 - 3 e^1 + 4 e^2
Display of an alternating form of degree 2 on a rank-3 free module::
sage: b = M.alternating_form(2, 'b', latex_name=r'\beta')
sage: b[0,1], b[0,2], b[1,2] = 3, 2, -1
sage: b.display()
b = 3 e^0/\e^1 + 2 e^0/\e^2 - e^1/\e^2
sage: latex(b.display()) # display in the notebook
\beta = 3 e^0\wedge e^1 + 2 e^0\wedge e^2 -e^1\wedge e^2
Display of an alternating form of degree 3 on a rank-3 free module::
sage: c = M.alternating_form(3, 'c')
sage: c[0,1,2] = 4
sage: c.display()
c = 4 e^0/\e^1/\e^2
sage: latex(c.display())
c = 4 e^0\wedge e^1\wedge e^2
Display of a vanishing alternating form::
sage: c[0,1,2] = 0 # the only independent component set to zero
sage: c.is_zero()
True
sage: c.display()
c = 0
sage: latex(c.display())
c = 0
sage: c[0,1,2] = 4 # value restored for what follows
Display in a basis which is not the default one::
sage: aut = M.automorphism(matrix=[[0,1,0], [0,0,-1], [1,0,0]],
....: basis=e)
sage: f = e.new_basis(aut, 'f')
sage: a.display(f)
a = 4 f^0 + f^1 + 3 f^2
sage: a.disp(f) # shortcut notation
a = 4 f^0 + f^1 + 3 f^2
sage: b.display(f)
b = -2 f^0/\f^1 - f^0/\f^2 - 3 f^1/\f^2
sage: c.display(f)
c = -4 f^0/\f^1/\f^2
The output format can be set via the argument ``output_formatter``
passed at the module construction::
sage: N = FiniteRankFreeModule(QQ, 3, name='N', start_index=1,
....: output_formatter=Rational.numerical_approx)
sage: e = N.basis('e')
sage: b = N.alternating_form(2, 'b')
sage: b[1,2], b[1,3], b[2,3] = 1/3, 5/2, 4
sage: b.display() # default format (53 bits of precision)
b = 0.333333333333333 e^1/\e^2 + 2.50000000000000 e^1/\e^3
+ 4.00000000000000 e^2/\e^3
The output format is then controlled by the argument ``format_spec`` of
the method :meth:`display`::
sage: b.display(format_spec=10) # 10 bits of precision
b = 0.33 e^1/\e^2 + 2.5 e^1/\e^3 + 4.0 e^2/\e^3
Check that the bug reported in :trac:`22520` is fixed::
sage: M = FiniteRankFreeModule(SR, 2, name='M')
sage: e = M.basis('e')
sage: a = M.alternating_form(2)
sage: a[0,1] = SR.var('t', domain='real')
sage: a.display()
t e^0/\e^1
"""
from sage.misc.latex import latex
from sage.tensor.modules.format_utilities import is_atomic, \
FormattedExpansion
if basis is None:
basis = self._fmodule._def_basis
cobasis = basis.dual_basis()
comp = self.comp(basis)
terms_txt = []
terms_latex = []
for ind in comp.non_redundant_index_generator():
ind_arg = ind + (format_spec,)
coef = comp[ind_arg]
if not (coef == 0): # NB: coef != 0 would return False for
# cases in which Sage cannot conclude
# see :trac:`22520`
bases_txt = []
bases_latex = []
for k in range(self._tensor_rank):
bases_txt.append(cobasis[ind[k]]._name)
bases_latex.append(latex(cobasis[ind[k]]))
basis_term_txt = "/\\".join(bases_txt)
basis_term_latex = r"\wedge ".join(bases_latex)
coef_txt = repr(coef)
if coef_txt == "1":
terms_txt.append(basis_term_txt)
terms_latex.append(basis_term_latex)
elif coef_txt == "-1":
terms_txt.append("-" + basis_term_txt)
terms_latex.append("-" + basis_term_latex)
else:
coef_latex = latex(coef)
if is_atomic(coef_txt):
terms_txt.append(coef_txt + " " + basis_term_txt)
else:
terms_txt.append("(" + coef_txt + ") " +
basis_term_txt)
if is_atomic(coef_latex):
terms_latex.append(coef_latex + basis_term_latex)
else:
terms_latex.append(r"\left(" + coef_latex + \
r"\right)" + basis_term_latex)
if not terms_txt:
expansion_txt = "0"
else:
expansion_txt = terms_txt[0]
for term in terms_txt[1:]:
if term[0] == "-":
expansion_txt += " - " + term[1:]
else:
expansion_txt += " + " + term
if not terms_latex:
expansion_latex = "0"
else:
expansion_latex = terms_latex[0]
for term in terms_latex[1:]:
if term[0] == "-":
expansion_latex += term
else:
expansion_latex += "+" + term
if self._name is None:
resu_txt = expansion_txt
else:
resu_txt = self._name + " = " + expansion_txt
if self._latex_name is None:
resu_latex = expansion_latex
else:
resu_latex = latex(self) + " = " + expansion_latex
return FormattedExpansion(resu_txt, resu_latex)
def wedge(self, other):
r"""
Exterior product with another differential form.
INPUT:
- ``other`` -- another differential form (on the same manifold)
OUTPUT:
- a :class:`DiffForm` of the exterior product ``self/\other``
EXAMPLES:
Exterior product of two 1-forms on the 2-sphere::
sage: M = Manifold(2, 'S^2', start_index=1) # the 2-dimensional sphere S^2
sage: U = M.open_subset('U') ; V = M.open_subset('V')
sage: M.declare_union(U,V) # S^2 is the union of U and V
sage: c_xy.<x,y> = U.chart() ; c_uv.<u,v> = V.chart() # stereographic coord. (North and South)
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: W = U.intersection(V) # The complement of the two poles
sage: e_xy = c_xy.frame() ; e_uv = c_uv.frame()
sage: a = M.diff_form(1, name='a')
sage: a[e_xy,:] = y, x
sage: a.add_comp_by_continuation(e_uv, W, c_uv)
sage: b = M.diff_form(1, name='b')
sage: b[e_xy,:] = x^2 + y^2, y
sage: b.add_comp_by_continuation(e_uv, W, c_uv)
sage: c = a.wedge(b); c
2-form a/\b on the 2-dimensional differentiable manifold S^2
sage: c.display(e_xy)
a/\b = (-x^3 - (x - 1)*y^2) dx/\dy
sage: c.display(e_uv)
a/\b = -(v^2 - u)/(u^8 + 4*u^6*v^2 + 6*u^4*v^4 + 4*u^2*v^6 + v^8) du/\dv
"""
from sage.tensor.modules.free_module_alt_form import FreeModuleAltForm
from sage.tensor.modules.format_utilities import is_atomic
if self._domain.is_subset(other._domain):
if not self._ambient_domain.is_subset(other._ambient_domain):
raise ValueError("incompatible ambient domains for exterior product")
elif other._domain.is_subset(self._domain):
if not other._ambient_domain.is_subset(self._ambient_domain):
raise ValueError("incompatible ambient domains for exterior product")
dom_resu = self._domain.intersection(other._domain)
ambient_dom_resu = self._ambient_domain.intersection(other._ambient_domain)
self_r = self.restrict(dom_resu)
other_r = other.restrict(dom_resu)
if ambient_dom_resu.is_manifestly_parallelizable():
# call of the FreeModuleAltForm version:
return FreeModuleAltForm.wedge(self_r, other_r)
# otherwise, the result is created here:
if self._name is not None and other._name is not None:
sname = self._name
oname = other._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
resu_name = sname + '/\\' + oname
if self._latex_name is not None and other._latex_name is not None:
slname = self._latex_name
olname = other._latex_name
if not is_atomic(slname):
slname = '(' + slname + ')'
if not is_atomic(olname):
olname = '(' + olname + ')'
resu_latex_name = slname + r'\wedge ' + olname
dest_map = self._vmodule._dest_map
dest_map_resu = dest_map.restrict(dom_resu,
subcodomain=ambient_dom_resu)
vmodule = dom_resu.vector_field_module(dest_map=dest_map_resu)
resu_degree = self._tensor_rank + other._tensor_rank
resu = vmodule.alternating_form(resu_degree, name=resu_name,
latex_name=resu_latex_name)
for dom in self_r._restrictions:
if dom in other_r._restrictions:
resu._restrictions[dom] = self_r._restrictions[dom].wedge(
other_r._restrictions[dom])
return resu
def display(self, basis=None, format_spec=None):
r"""
Display the alternating contravariant tensor ``self`` in terms
of its expansion w.r.t. a given module basis.
The expansion is actually performed onto exterior products of
elements of ``basis`` (see examples below). The output is either
text-formatted (console mode) or LaTeX-formatted (notebook mode).
INPUT:
- ``basis`` -- (default: ``None``) basis of the free module with
respect to which ``self`` is expanded; if none is provided,
the module's default basis is assumed
- ``format_spec`` -- (default: ``None``) format specification
passed to ``self._fmodule._output_formatter`` to format the
output
EXAMPLES:
Display of an alternating contravariant tensor of degree 2 on a rank-3
free module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = M.alternating_contravariant_tensor(2, 'a', latex_name=r'\alpha')
sage: a[0,1], a[0,2], a[1,2] = 3, 2, -1
sage: a.display()
a = 3 e_0/\e_1 + 2 e_0/\e_2 - e_1/\e_2
sage: latex(a.display()) # display in the notebook
\alpha = 3 e_{0}\wedge e_{1} + 2 e_{0}\wedge e_{2} -e_{1}\wedge e_{2}
Display of an alternating contravariant tensor of degree 3 on a rank-3
free module::
sage: b = M.alternating_contravariant_tensor(3, 'b')
sage: b[0,1,2] = 4
sage: b.display()
b = 4 e_0/\e_1/\e_2
sage: latex(b.display())
b = 4 e_{0}\wedge e_{1}\wedge e_{2}
Display of a vanishing alternating contravariant tensor::
sage: b[0,1,2] = 0 # the only independent component set to zero
sage: b.is_zero()
True
sage: b.display()
b = 0
sage: latex(b.display())
b = 0
sage: b[0,1,2] = 4 # value restored for what follows
Display in a basis which is not the default one::
sage: aut = M.automorphism(matrix=[[0,1,0], [0,0,-1], [1,0,0]],
....: basis=e)
sage: f = e.new_basis(aut, 'f')
sage: a.display(f)
a = -2 f_0/\f_1 - f_0/\f_2 - 3 f_1/\f_2
sage: a.disp(f) # shortcut notation
a = -2 f_0/\f_1 - f_0/\f_2 - 3 f_1/\f_2
sage: b.display(f)
b = -4 f_0/\f_1/\f_2
The output format can be set via the argument ``output_formatter``
passed at the module construction::
sage: N = FiniteRankFreeModule(QQ, 3, name='N', start_index=1,
....: output_formatter=Rational.numerical_approx)
sage: e = N.basis('e')
sage: a = N.alternating_contravariant_tensor(2, 'a')
sage: a[1,2], a[1,3], a[2,3] = 1/3, 5/2, 4
sage: a.display() # default format (53 bits of precision)
a = 0.333333333333333 e_1/\e_2 + 2.50000000000000 e_1/\e_3
+ 4.00000000000000 e_2/\e_3
The output format is then controlled by the argument ``format_spec`` of
the method :meth:`display`::
sage: a.display(format_spec=10) # 10 bits of precision
a = 0.33 e_1/\e_2 + 2.5 e_1/\e_3 + 4.0 e_2/\e_3
"""
from sage.misc.latex import latex
from sage.tensor.modules.format_utilities import (is_atomic,
FormattedExpansion)
basis, format_spec = self._preparse_display(basis=basis,
format_spec=format_spec)
comp = self.comp(basis)
terms_txt = []
terms_latex = []
for ind in comp.non_redundant_index_generator():
ind_arg = ind + (format_spec, )
coef = comp[ind_arg]
# Check whether the coefficient is zero, preferably via
# the fast method is_trivial_zero():
if hasattr(coef, 'is_trivial_zero'):
zero_coef = coef.is_trivial_zero()
else:
zero_coef = coef == 0
if not zero_coef:
bases_txt = []
bases_latex = []
for k in range(self._tensor_rank):
bases_txt.append(basis[ind[k]]._name)
bases_latex.append(latex(basis[ind[k]]))
basis_term_txt = "/\\".join(bases_txt)
basis_term_latex = r"\wedge ".join(bases_latex)
coef_txt = repr(coef)
if coef_txt == "1":
terms_txt.append(basis_term_txt)
terms_latex.append(basis_term_latex)
elif coef_txt == "-1":
terms_txt.append("-" + basis_term_txt)
terms_latex.append("-" + basis_term_latex)
else:
coef_latex = latex(coef)
if is_atomic(coef_txt):
terms_txt.append(coef_txt + " " + basis_term_txt)
else:
terms_txt.append("(" + coef_txt + ") " +
basis_term_txt)
if is_atomic(coef_latex):
terms_latex.append(coef_latex + basis_term_latex)
else:
terms_latex.append(r"\left(" + coef_latex + \
r"\right)" + basis_term_latex)
if not terms_txt:
expansion_txt = "0"
else:
expansion_txt = terms_txt[0]
for term in terms_txt[1:]:
if term[0] == "-":
expansion_txt += " - " + term[1:]
else:
expansion_txt += " + " + term
if not terms_latex:
expansion_latex = "0"
else:
expansion_latex = terms_latex[0]
for term in terms_latex[1:]:
if term[0] == "-":
expansion_latex += term
else:
expansion_latex += "+" + term
if self._name is None:
resu_txt = expansion_txt
else:
resu_txt = self._name + " = " + expansion_txt
if self._latex_name is None:
resu_latex = expansion_latex
else:
resu_latex = latex(self) + " = " + expansion_latex
return FormattedExpansion(resu_txt, resu_latex)
def wedge(self, other):
r"""
Exterior product of ``self`` with the alternating form ``other``.
INPUT:
- ``other`` -- an alternating form
OUTPUT:
- instance of :class:`FreeModuleAltForm` representing the exterior
product ``self/\other``
EXAMPLES:
Exterior product of two linear forms::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: a = M.linear_form('A')
sage: a[:] = [1,-3,4]
sage: b = M.linear_form('B')
sage: b[:] = [2,-1,2]
sage: c = a.wedge(b) ; c
Alternating form A/\B of degree 2 on the Rank-3 free module M
over the Integer Ring
sage: c.display()
A/\B = 5 e^0/\e^1 - 6 e^0/\e^2 - 2 e^1/\e^2
sage: latex(c)
A\wedge B
sage: latex(c.display())
A\wedge B = 5 e^{0}\wedge e^{1} -6 e^{0}\wedge e^{2} -2 e^{1}\wedge e^{2}
Test of the computation::
sage: a.wedge(b) == a*b - b*a
True
Exterior product of a linear form and an alternating form of degree 2::
sage: d = M.linear_form('D')
sage: d[:] = [-1,2,4]
sage: s = d.wedge(c) ; s
Alternating form D/\A/\B of degree 3 on the Rank-3 free module M
over the Integer Ring
sage: s.display()
D/\A/\B = 34 e^0/\e^1/\e^2
Test of the computation::
sage: s[0,1,2] == d[0]*c[1,2] + d[1]*c[2,0] + d[2]*c[0,1]
True
Let us check that the exterior product is associative::
sage: d.wedge(a.wedge(b)) == (d.wedge(a)).wedge(b)
True
and that it is graded anticommutative::
sage: a.wedge(b) == - b.wedge(a)
True
sage: d.wedge(c) == c.wedge(d)
True
"""
from .format_utilities import is_atomic
if not isinstance(other, FreeModuleAltForm):
raise TypeError("the second argument for the exterior product " +
"must be an alternating form")
if other._tensor_rank == 0:
return other*self
if self._tensor_rank == 0:
return self*other
fmodule = self._fmodule
basis = self.common_basis(other)
if basis is None:
raise ValueError("no common basis for the exterior product")
rank_r = self._tensor_rank + other._tensor_rank
cmp_s = self._components[basis]
cmp_o = other._components[basis]
cmp_r = CompFullyAntiSym(fmodule._ring, basis, rank_r,
start_index=fmodule._sindex,
output_formatter=fmodule._output_formatter)
for ind_s, val_s in cmp_s._comp.items():
for ind_o, val_o in cmp_o._comp.items():
ind_r = ind_s + ind_o
if len(ind_r) == len(set(ind_r)): # all indices are different
cmp_r[[ind_r]] += val_s * val_o
result = fmodule.alternating_form(rank_r)
result._components[basis] = cmp_r
if self._name is not None and other._name is not None:
sname = self._name
oname = other._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
result._name = sname + '/\\' + oname
if self._latex_name is not None and other._latex_name is not None:
slname = self._latex_name
olname = other._latex_name
if not is_atomic(slname):
slname = '(' + slname + ')'
if not is_atomic(olname):
olname = '(' + olname + ')'
result._latex_name = slname + r'\wedge ' + olname
return result
def interior_product(self, alt_tensor):
r"""
Interior product with an alternating contravariant tensor.
If ``self`` is an alternating form `A` of degree `p` and `B` is an
alternating contravariant tensor of degree `q\geq p` on the same free
module, the interior product of `A` by `B` is the alternating
contravariant tensor `\iota_A B` of degree `q-p` defined by
.. MATH::
(\iota_A B)^{i_1\ldots i_{q-p}} = A_{k_1\ldots k_p}
B^{k_1\ldots k_p i_1\ldots i_{q-p}}
.. NOTE::
``A.interior_product(B)`` yields the same result as
``A.contract(0,..., p-1, B, 0,..., p-1)`` (cf.
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.contract`),
but ``interior_product`` is more efficient, the alternating
character of `A` being not used to reduce the computation in
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.contract`
INPUT:
- ``alt_tensor`` -- alternating contravariant tensor `B` (instance of
:class:`~sage.tensor.modules.alternating_contr_tensor.AlternatingContrTensor`);
the degree of `B` must be at least equal to the degree of ``self``
OUTPUT:
- element of the base ring (case `p=q`) or
:class:`~sage.tensor.modules.alternating_contr_tensor.AlternatingContrTensor`
(case `p<q`) representing the interior product `\iota_A B`, where `A`
is ``self``
.. SEEALSO::
:meth:`~sage.tensor.modules.alternating_contr_tensor.AlternatingContrTensor.interior_product`
for the interior product of an alternating contravariant tensor by
an alternating form
EXAMPLES:
Let us consider a rank-3 free module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M', start_index=1)
sage: e = M.basis('e')
and various interior products on it, starting with a linear form
(``p=1``) and a module element (``q=1``)::
sage: a = M.linear_form(name='A')
sage: a[:] = [-2, 4, 3]
sage: b = M([3, 1, 5], basis=e, name='B')
sage: c = a.interior_product(b); c
13
sage: c == a.contract(b)
True
Case ``p=1`` and ``q=2``::
sage: b = M.alternating_contravariant_tensor(2, name='B')
sage: b[1,2], b[1,3], b[2,3] = 5, 2, 3
sage: c = a.interior_product(b); c
Element i_A B of the Rank-3 free module M over the Integer Ring
sage: c.display()
i_A B = -26 e_1 - 19 e_2 + 8 e_3
sage: latex(c)
\iota_{A} B
sage: c == a.contract(b)
True
Case ``p=1`` and ``q=3``::
sage: b = M.alternating_contravariant_tensor(3, name='B')
sage: b[1,2,3] = 5
sage: c = a.interior_product(b); c
Alternating contravariant tensor i_A B of degree 2 on the Rank-3 free module M over the Integer Ring
sage: c.display()
i_A B = 15 e_1/\e_2 - 20 e_1/\e_3 - 10 e_2/\e_3
sage: c == a.contract(b)
True
Case ``p=2`` and ``q=2``::
sage: a = M.alternating_form(2, name='A')
sage: a[1,2], a[1,3], a[2,3] = 2, -3, 1
sage: b = M.alternating_contravariant_tensor(2, name='B')
sage: b[1,2], b[1,3], b[2,3] = 5, 2, 3
sage: c = a.interior_product(b); c
14
sage: c == a.contract(0, 1, b, 0, 1) # contraction on all indices of a
True
Case ``p=2`` and ``q=3``::
sage: b = M.alternating_contravariant_tensor(3, name='B')
sage: b[1,2,3] = 5
sage: c = a.interior_product(b); c
Element i_A B of the Rank-3 free module M over the Integer Ring
sage: c.display()
i_A B = 10 e_1 + 30 e_2 + 20 e_3
sage: c == a.contract(0, 1, b, 0, 1)
True
Case ``p=3`` and ``q=3``::
sage: a = M.alternating_form(3, name='A')
sage: a[1,2,3] = -2
sage: c = a.interior_product(b); c
-60
sage: c == a.contract(0, 1, 2, b, 0, 1, 2)
True
"""
from .format_utilities import is_atomic
from .alternating_contr_tensor import AlternatingContrTensor
if not isinstance(alt_tensor, AlternatingContrTensor):
raise TypeError("{} is not an alternating ".format(alt_tensor) +
"contravariant tensor")
p_res = alt_tensor._tensor_rank - self._tensor_rank # degree of result
if self._tensor_rank == 1:
# Case p = 1:
res = self.contract(alt_tensor) # contract() deals efficiently
# with antisymmetry for p = 1
else:
# Case p > 1:
if alt_tensor._fmodule != self._fmodule:
raise ValueError("{} is not defined on ".format(alt_tensor) +
"the same module as the {}".format(self))
if alt_tensor._tensor_rank < self._tensor_rank:
raise ValueError("the degree of the {} ".format(alt_tensor) +
"is lower than that of the {}".format(self))
# Interior product at the component level:
basis = self.common_basis(alt_tensor)
if basis is None:
raise ValueError("no common basis for the interior product")
comp = self._components[basis].interior_product(
alt_tensor._components[basis])
if p_res == 0:
res = comp # result is a scalar
else:
res = self._fmodule.tensor_from_comp((p_res, 0), comp)
# Name of the result
res_name = None
if self._name is not None and alt_tensor._name is not None:
sname = self._name
oname = alt_tensor._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
res_name = 'i_' + sname + ' ' + oname
res_latex_name = None
if self._latex_name is not None and alt_tensor._latex_name is not None:
slname = self._latex_name
olname = alt_tensor._latex_name
if not is_atomic(olname):
olname = r'\left(' + olname + r'\right)'
res_latex_name = r'\iota_{' + slname + '} ' + olname
if p_res == 0:
if res_name:
try: # there is no guarantee that base ring elements have
# set_name
res.set_name(res_name, latex_name=res_latex_name)
except (AttributeError, TypeError):
pass
else:
res.set_name(res_name, latex_name=res_latex_name)
return res
def interior_product(self, form):
r"""
Interior product with an alternating form.
If ``self`` is an alternating contravariant tensor `A` of degree `p`
and `B` is an alternating form of degree `q\geq p` on the same free
module, the interior product of `A` by `B` is the alternating form
`\iota_A B` of degree `q-p` defined by
.. MATH::
(\iota_A B)_{i_1\ldots i_{q-p}} = A^{k_1\ldots k_p}
B_{k_1\ldots k_p i_1\ldots i_{q-p}}
.. NOTE::
``A.interior_product(B)`` yields the same result as
``A.contract(0,..., p-1, B, 0,..., p-1)`` (cf.
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.contract`),
but ``interior_product`` is more efficient, the alternating
character of `A` being not used to reduce the computation in
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.contract`
INPUT:
- ``form`` -- alternating form `B` (instance of
:class:`~sage.tensor.modules.free_module_alt_form.FreeModuleAltForm`);
the degree of `B` must be at least equal to the degree of ``self``
OUTPUT:
- element of the base ring (case `p=q`) or
:class:`~sage.tensor.modules.free_module_alt_form.FreeModuleAltForm`
(case `p<q`) representing the interior product `\iota_A B`, where `A`
is ``self``
.. SEEALSO::
:meth:`~sage.tensor.modules.free_module_alt_form.FreeModuleAltForm.interior_product`
for the interior product of an alternating form by an alternating
contravariant tensor
EXAMPLES:
Let us consider a rank-4 free module::
sage: M = FiniteRankFreeModule(ZZ, 4, name='M', start_index=1)
sage: e = M.basis('e')
and various interior products on it, starting with a module element
(``p=1``) and a linear form (``q=1``)::
sage: a = M([-2,1,2,3], basis=e, name='A')
sage: b = M.linear_form(name='B')
sage: b[:] = [2, 0, -3, 4]
sage: c = a.interior_product(b); c
2
sage: c == a.contract(b)
True
Case ``p=1`` and ``q=3``::
sage: b = M.alternating_form(3, name='B')
sage: b[1,2,3], b[1,2,4], b[1,3,4], b[2,3,4] = 3, -1, 2, 5
sage: c = a.interior_product(b); c
Alternating form i_A B of degree 2 on the Rank-4 free module M over the Integer Ring
sage: c.display()
i_A B = 3 e^1/\e^2 + 3 e^1/\e^3 - 3 e^1/\e^4 + 9 e^2/\e^3 - 8 e^2/\e^4 + e^3/\e^4
sage: latex(c)
\iota_{A} B
sage: c == a.contract(b)
True
Case ``p=2`` and ``q=3``::
sage: a = M.alternating_contravariant_tensor(2, name='A')
sage: a[1,2], a[1,3], a[1,4] = 2, -5, 3
sage: a[2,3], a[2,4], a[3,4] = -1, 4, 2
sage: c = a.interior_product(b); c
Linear form i_A B on the Rank-4 free module M over the Integer Ring
sage: c.display()
i_A B = -6 e^1 + 56 e^2 - 40 e^3 - 34 e^4
sage: c == a.contract(0, 1, b, 0, 1) # contraction on all indices of a
True
Case ``p=2`` and ``q=4``::
sage: b = M.alternating_form(4, name='B')
sage: b[1,2,3,4] = 5
sage: c = a.interior_product(b); c
Alternating form i_A B of degree 2 on the Rank-4 free module M over the Integer Ring
sage: c.display()
i_A B = 20 e^1/\e^2 - 40 e^1/\e^3 - 10 e^1/\e^4 + 30 e^2/\e^3 + 50 e^2/\e^4 + 20 e^3/\e^4
sage: c == a.contract(0, 1, b, 0, 1)
True
Case ``p=2`` and ``q=2``::
sage: b = M.alternating_form(2)
sage: b[1,2], b[1,3], b[1,4] = 6, 0, -2
sage: b[2,3], b[2,4], b[3,4] = 2, 3, 4
sage: c = a.interior_product(b); c
48
sage: c == a.contract(0, 1, b, 0, 1)
True
Case ``p=3`` and ``q=3``::
sage: a = M.alternating_contravariant_tensor(3, name='A')
sage: a[1,2,3], a[1,2,4], a[1,3,4], a[2,3,4] = -3, 2, 8, -5
sage: b = M.alternating_form(3, name='B')
sage: b[1,2,3], b[1,2,4], b[1,3,4], b[2,3,4] = 3, -1, 2, 5
sage: c = a.interior_product(b); c
-120
sage: c == a.contract(0, 1, 2, b, 0, 1, 2)
True
Case ``p=3`` and ``q=4``::
sage: b = M.alternating_form(4, name='B')
sage: b[1,2,3,4] = 5
sage: c = a.interior_product(b); c
Linear form i_A B on the Rank-4 free module M over the Integer Ring
sage: c.display()
i_A B = 150 e^1 + 240 e^2 - 60 e^3 - 90 e^4
sage: c == a.contract(0, 1, 2, b, 0, 1, 2)
True
Case ``p=4`` and ``q=4``::
sage: a = M.alternating_contravariant_tensor(4, name='A')
sage: a[1,2,3,4] = -2
sage: c = a.interior_product(b); c
-240
sage: c == a.contract(0, 1, 2, 3, b, 0, 1, 2, 3)
True
"""
from .format_utilities import is_atomic
from .free_module_alt_form import FreeModuleAltForm
if not isinstance(form, FreeModuleAltForm):
raise TypeError("{} is not an alternating form".format(form))
p_res = form._tensor_rank - self._tensor_rank # degree of the result
if self._tensor_rank == 1:
# Case p = 1:
res = self.contract(form) # contract() deals efficiently with
# the antisymmetry for p = 1
else:
# Case p > 1:
if form._fmodule != self._fmodule:
raise ValueError("{} is not defined on the same ".format(form) +
"module as the {}".format(self))
if form._tensor_rank < self._tensor_rank:
raise ValueError("the degree of the {} is lower ".format(form) +
"than that of the {}".format(self))
# Interior product at the component level:
basis = self.common_basis(form)
if basis is None:
raise ValueError("no common basis for the interior product")
comp = self._components[basis].interior_product(
form._components[basis])
if p_res == 0:
res = comp # result is a scalar
else:
res = self._fmodule.tensor_from_comp((0, p_res), comp)
# Name of the result
res_name = None
if self._name is not None and form._name is not None:
sname = self._name
oname = form._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
res_name = 'i_' + sname + ' ' + oname
res_latex_name = None
if self._latex_name is not None and form._latex_name is not None:
slname = self._latex_name
olname = form._latex_name
if not is_atomic(olname):
olname = r'\left(' + olname + r'\right)'
res_latex_name = r'\iota_{' + slname + '} ' + olname
if p_res == 0:
if res_name:
try: # there is no guarantee that base ring elements have
# set_name
res.set_name(res_name, latex_name=res_latex_name)
except (AttributeError, TypeError):
pass
else:
res.set_name(res_name, latex_name=res_latex_name)
return res
def display(self, basis=None, format_spec=None):
r"""
Display the alternating form ``self`` in terms of its expansion w.r.t.
a given module basis.
The expansion is actually performed onto exterior products of elements
of the cobasis (dual basis) associated with ``basis`` (see examples
below). The output is either text-formatted (console mode) or
LaTeX-formatted (notebook mode).
INPUT:
- ``basis`` -- (default: ``None``) basis of the free module with
respect to which the alternating form is expanded; if none is
provided, the module's default basis is assumed
- ``format_spec`` -- (default: ``None``) format specification passed
to ``self._fmodule._output_formatter`` to format the output
EXAMPLES:
Display of an alternating form of degree 1 (linear form) on a rank-3
free module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: e.dual_basis()
Dual basis (e^0,e^1,e^2) on the Rank-3 free module M over the Integer Ring
sage: a = M.linear_form('a', latex_name=r'\alpha')
sage: a[:] = [1,-3,4]
sage: a.display(e)
a = e^0 - 3 e^1 + 4 e^2
sage: a.display() # a shortcut since e is M's default basis
a = e^0 - 3 e^1 + 4 e^2
sage: latex(a.display()) # display in the notebook
\alpha = e^{0} -3 e^{1} + 4 e^{2}
A shortcut is ``disp()``::
sage: a.disp()
a = e^0 - 3 e^1 + 4 e^2
Display of an alternating form of degree 2 on a rank-3 free module::
sage: b = M.alternating_form(2, 'b', latex_name=r'\beta')
sage: b[0,1], b[0,2], b[1,2] = 3, 2, -1
sage: b.display()
b = 3 e^0/\e^1 + 2 e^0/\e^2 - e^1/\e^2
sage: latex(b.display()) # display in the notebook
\beta = 3 e^{0}\wedge e^{1} + 2 e^{0}\wedge e^{2} -e^{1}\wedge e^{2}
Display of an alternating form of degree 3 on a rank-3 free module::
sage: c = M.alternating_form(3, 'c')
sage: c[0,1,2] = 4
sage: c.display()
c = 4 e^0/\e^1/\e^2
sage: latex(c.display())
c = 4 e^{0}\wedge e^{1}\wedge e^{2}
Display of a vanishing alternating form::
sage: c[0,1,2] = 0 # the only independent component set to zero
sage: c.is_zero()
True
sage: c.display()
c = 0
sage: latex(c.display())
c = 0
sage: c[0,1,2] = 4 # value restored for what follows
Display in a basis which is not the default one::
sage: aut = M.automorphism(matrix=[[0,1,0], [0,0,-1], [1,0,0]],
....: basis=e)
sage: f = e.new_basis(aut, 'f')
sage: a.display(f)
a = 4 f^0 + f^1 + 3 f^2
sage: a.disp(f) # shortcut notation
a = 4 f^0 + f^1 + 3 f^2
sage: b.display(f)
b = -2 f^0/\f^1 - f^0/\f^2 - 3 f^1/\f^2
sage: c.display(f)
c = -4 f^0/\f^1/\f^2
The output format can be set via the argument ``output_formatter``
passed at the module construction::
sage: N = FiniteRankFreeModule(QQ, 3, name='N', start_index=1,
....: output_formatter=Rational.numerical_approx)
sage: e = N.basis('e')
sage: b = N.alternating_form(2, 'b')
sage: b[1,2], b[1,3], b[2,3] = 1/3, 5/2, 4
sage: b.display() # default format (53 bits of precision)
b = 0.333333333333333 e^1/\e^2 + 2.50000000000000 e^1/\e^3
+ 4.00000000000000 e^2/\e^3
The output format is then controlled by the argument ``format_spec`` of
the method :meth:`display`::
sage: b.display(format_spec=10) # 10 bits of precision
b = 0.33 e^1/\e^2 + 2.5 e^1/\e^3 + 4.0 e^2/\e^3
Check that the bug reported in :trac:`22520` is fixed::
sage: M = FiniteRankFreeModule(SR, 2, name='M')
sage: e = M.basis('e')
sage: a = M.alternating_form(2)
sage: a[0,1] = SR.var('t', domain='real')
sage: a.display()
t e^0/\e^1
"""
from sage.misc.latex import latex
from sage.tensor.modules.format_utilities import is_atomic, \
FormattedExpansion
if basis is None:
basis = self._fmodule._def_basis
cobasis = basis.dual_basis()
comp = self.comp(basis)
terms_txt = []
terms_latex = []
for ind in comp.non_redundant_index_generator():
ind_arg = ind + (format_spec,)
coef = comp[ind_arg]
# Check whether the coefficient is zero, preferably via
# the fast method is_trivial_zero():
if hasattr(coef, 'is_trivial_zero'):
zero_coef = coef.is_trivial_zero()
else:
zero_coef = coef == 0
if not zero_coef:
bases_txt = []
bases_latex = []
for k in range(self._tensor_rank):
bases_txt.append(cobasis[ind[k]]._name)
bases_latex.append(latex(cobasis[ind[k]]))
basis_term_txt = "/\\".join(bases_txt)
basis_term_latex = r"\wedge ".join(bases_latex)
coef_txt = repr(coef)
if coef_txt == "1":
terms_txt.append(basis_term_txt)
terms_latex.append(basis_term_latex)
elif coef_txt == "-1":
terms_txt.append("-" + basis_term_txt)
terms_latex.append("-" + basis_term_latex)
else:
coef_latex = latex(coef)
if is_atomic(coef_txt):
terms_txt.append(coef_txt + " " + basis_term_txt)
else:
terms_txt.append("(" + coef_txt + ") " +
basis_term_txt)
if is_atomic(coef_latex):
terms_latex.append(coef_latex + basis_term_latex)
else:
terms_latex.append(r"\left(" + coef_latex + \
r"\right)" + basis_term_latex)
if not terms_txt:
expansion_txt = "0"
else:
expansion_txt = terms_txt[0]
for term in terms_txt[1:]:
if term[0] == "-":
expansion_txt += " - " + term[1:]
else:
expansion_txt += " + " + term
if not terms_latex:
expansion_latex = "0"
else:
expansion_latex = terms_latex[0]
for term in terms_latex[1:]:
if term[0] == "-":
expansion_latex += term
else:
expansion_latex += "+" + term
if self._name is None:
resu_txt = expansion_txt
else:
resu_txt = self._name + " = " + expansion_txt
if self._latex_name is None:
resu_latex = expansion_latex
else:
resu_latex = latex(self) + " = " + expansion_latex
return FormattedExpansion(resu_txt, resu_latex)
def _sub_(self, other):
r"""
Subtraction of two mixed forms.
INPUT:
- ``other`` -- a mixed form, in the same algebra as ``self``
OUTPUT:
- the mixed form resulting from the subtraction of ``self``
and ``other``
TESTS::
sage: M = Manifold(2, 'M')
sage: U = M.open_subset('U') ; V = M.open_subset('V')
sage: M.declare_union(U,V) # M is the union of U and V
sage: c_xy.<x,y> = U.chart() ; c_uv.<u,v> = V.chart()
sage: xy_to_uv = c_xy.transition_map(c_uv, (x+y, x-y),
....: intersection_name='W', restrictions1= x>0,
....: restrictions2= u+v>0)
sage: uv_to_xy = xy_to_uv.inverse()
sage: e_xy = c_xy.frame(); e_uv = c_uv.frame()
sage: f = M.scalar_field(x, name='f')
sage: a = M.diff_form(1, name='a')
sage: a[e_xy,0] = x
sage: A = M.mixed_form(name='A', comp=[f, a, 0])
sage: A.add_comp_by_continuation(e_uv, U.intersection(V), c_uv)
sage: g = M.scalar_field(u, name='g', chart=c_uv)
sage: b = M.diff_form(1, name='b')
sage: b[e_uv,1] = v
sage: B = M.mixed_form(name='B', comp=[g, b, 0])
sage: B.add_comp_by_continuation(e_xy, V.intersection(U), c_xy)
sage: C = A._sub_(B); C
Mixed differential form A-B on the 2-dimensional differentiable
manifold M
sage: A.display(e_uv)
A = [1/2*u + 1/2*v] + [(1/4*u + 1/4*v) du + (1/4*u + 1/4*v) dv] + [0]
sage: B.display(e_xy)
B = [x + y] + [(x - y) dx + (-x + y) dy] + [0]
sage: C.display(e_xy)
A-B = [-y] + [y dx + (x - y) dy] + [0]
sage: C.display(e_uv)
A-B = [-1/2*u + 1/2*v] + [(1/4*u + 1/4*v) du + (1/4*u - 3/4*v) dv] + [0]
sage: C == A - B # indirect doctest
True
sage: Z = A.parent().zero(); Z
Mixed differential form zero on the 2-dimensional differentiable
manifold M
sage: A._sub_(Z) == A
True
sage: Z._sub_(A) == -A
True
"""
resu_comp = [self[j] - other[j] for j in range(self._max_deg + 1)]
resu = type(self)(self.parent(), comp=resu_comp)
# Compose name:
from sage.tensor.modules.format_utilities import is_atomic
if self._name is not None and other._name is not None:
sname = self._name
oname = other._name
if not is_atomic(oname):
oname = '(' + oname + ')'
resu._name = sname + '-' + oname
if self._latex_name is not None and other._latex_name is not None:
slname = self._latex_name
olname = other._latex_name
if not is_atomic(olname):
olname = '(' + olname + ')'
resu._latex_name = slname + '-' + olname
return resu
def _display_form(rst, basis, chart):
r"""
Display coordinate expression of a single form ``rst`` (without
equality sign).
This helper method is invoked by :meth:`display`.
TESTS::
sage: M = Manifold(2, 'M')
sage: c_xy.<x,y> = M.chart()
sage: omega = M.diff_form(1, name='omega')
sage: omega[c_xy.frame(),0] = x^2
sage: F = M.mixed_form(comp=[0,omega,0])
sage: F.disp(c_xy.frame())
[0] + [x^2 dx] + [0]
"""
from sage.tensor.modules.format_utilities import is_atomic
cobasis = basis.dual_basis()
comp = rst.comp(basis)
terms_txt = []
terms_latex = []
for ind in comp.non_redundant_index_generator():
ind_arg = ind + (chart, )
coef = comp[ind_arg]
# Check whether the coefficient is zero, preferably via
# the fast method is_trivial_zero():
if hasattr(coef, 'is_trivial_zero'):
zero_coef = coef.is_trivial_zero()
else:
zero_coef = coef == 0
if not zero_coef:
bases_txt = []
bases_latex = []
for k in range(rst._tensor_rank):
bases_txt.append(cobasis[ind[k]]._name)
bases_latex.append(latex(cobasis[ind[k]]))
basis_term_txt = "/\\".join(bases_txt)
basis_term_latex = r"\wedge ".join(bases_latex)
coef_txt = repr(coef)
if coef_txt == "1":
terms_txt.append(basis_term_txt)
terms_latex.append(basis_term_latex)
elif coef_txt == "-1":
terms_txt.append("-" + basis_term_txt)
terms_latex.append("-" + basis_term_latex)
else:
coef_latex = latex(coef)
if is_atomic(coef_txt):
terms_txt.append(coef_txt + " " + basis_term_txt)
else:
terms_txt.append("(" + coef_txt + ") " +
basis_term_txt)
if is_atomic(coef_latex):
terms_latex.append(coef_latex + basis_term_latex)
else:
terms_latex.append(r"\left(" + coef_latex +
r"\right)" + basis_term_latex)
if not terms_txt:
resu_txt = "0"
else:
resu_txt = terms_txt[0]
for term in terms_txt[1:]:
if term[0] == "-":
resu_txt += " - " + term[1:]
else:
resu_txt += " + " + term
if not terms_latex:
resu_latex = r"0"
else:
resu_latex = terms_latex[0]
for term in terms_latex[1:]:
if term[0] == "-":
resu_latex += term
else:
resu_latex += "+" + term
return FormattedExpansion(resu_txt, resu_latex)
def interior_product(self, alt_tensor):
r"""
Interior product with an alternating contravariant tensor.
If ``self`` is an alternating form `A` of degree `p` and `B` is an
alternating contravariant tensor of degree `q\geq p` on the same free
module, the interior product of `A` by `B` is the alternating
contravariant tensor `\iota_A B` of degree `q-p` defined by
.. MATH::
(\iota_A B)^{i_1\ldots i_{q-p}} = A_{k_1\ldots k_p}
B^{k_1\ldots k_p i_1\ldots i_{q-p}}
.. NOTE::
``A.interior_product(B)`` yields the same result as
``A.contract(0,..., p-1, B, 0,..., p-1)`` (cf.
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.contract`),
but ``interior_product`` is more efficient, the alternating
character of `A` being not used to reduce the computation in
:meth:`~sage.tensor.modules.free_module_tensor.FreeModuleTensor.contract`
INPUT:
- ``alt_tensor`` -- alternating contravariant tensor `B` (instance of
:class:`~sage.tensor.modules.alternating_contr_tensor.AlternatingContrTensor`);
the degree of `B` must be at least equal to the degree of ``self``
OUTPUT:
- element of the base ring (case `p=q`) or
:class:`~sage.tensor.modules.alternating_contr_tensor.AlternatingContrTensor`
(case `p<q`) representing the interior product `\iota_A B`, where `A`
is ``self``
.. SEEALSO::
:meth:`~sage.tensor.modules.alternating_contr_tensor.AlternatingContrTensor.interior_product`
for the interior product of an alternating contravariant tensor by
an alternating form
EXAMPLES:
Let us consider a rank-3 free module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M', start_index=1)
sage: e = M.basis('e')
and various interior products on it, starting with a linear form
(``p=1``) and a module element (``q=1``)::
sage: a = M.linear_form(name='A')
sage: a[:] = [-2, 4, 3]
sage: b = M([3, 1, 5], basis=e, name='B')
sage: c = a.interior_product(b); c
13
sage: c == a.contract(b)
True
Case ``p=1`` and ``q=2``::
sage: b = M.alternating_contravariant_tensor(2, name='B')
sage: b[1,2], b[1,3], b[2,3] = 5, 2, 3
sage: c = a.interior_product(b); c
Element i_A B of the Rank-3 free module M over the Integer Ring
sage: c.display()
i_A B = -26 e_1 - 19 e_2 + 8 e_3
sage: latex(c)
\iota_{A} B
sage: c == a.contract(b)
True
Case ``p=1`` and ``q=3``::
sage: b = M.alternating_contravariant_tensor(3, name='B')
sage: b[1,2,3] = 5
sage: c = a.interior_product(b); c
Alternating contravariant tensor i_A B of degree 2 on the Rank-3 free module M over the Integer Ring
sage: c.display()
i_A B = 15 e_1/\e_2 - 20 e_1/\e_3 - 10 e_2/\e_3
sage: c == a.contract(b)
True
Case ``p=2`` and ``q=2``::
sage: a = M.alternating_form(2, name='A')
sage: a[1,2], a[1,3], a[2,3] = 2, -3, 1
sage: b = M.alternating_contravariant_tensor(2, name='B')
sage: b[1,2], b[1,3], b[2,3] = 5, 2, 3
sage: c = a.interior_product(b); c
14
sage: c == a.contract(0, 1, b, 0, 1) # contraction on all indices of a
True
Case ``p=2`` and ``q=3``::
sage: b = M.alternating_contravariant_tensor(3, name='B')
sage: b[1,2,3] = 5
sage: c = a.interior_product(b); c
Element i_A B of the Rank-3 free module M over the Integer Ring
sage: c.display()
i_A B = 10 e_1 + 30 e_2 + 20 e_3
sage: c == a.contract(0, 1, b, 0, 1)
True
Case ``p=3`` and ``q=3``::
sage: a = M.alternating_form(3, name='A')
sage: a[1,2,3] = -2
sage: c = a.interior_product(b); c
-60
sage: c == a.contract(0, 1, 2, b, 0, 1, 2)
True
"""
from .format_utilities import is_atomic
from .alternating_contr_tensor import AlternatingContrTensor
if not isinstance(alt_tensor, AlternatingContrTensor):
raise TypeError("{} is not an alternating ".format(alt_tensor) +
"contravariant tensor")
p_res = alt_tensor._tensor_rank - self._tensor_rank # degree of result
if self._tensor_rank == 1:
# Case p = 1:
res = self.contract(alt_tensor) # contract() deals efficiently
# with antisymmetry for p = 1
else:
# Case p > 1:
if alt_tensor._fmodule != self._fmodule:
raise ValueError("{} is not defined on ".format(alt_tensor) +
"the same module as the {}".format(self))
if alt_tensor._tensor_rank < self._tensor_rank:
raise ValueError("the degree of the {} ".format(alt_tensor) +
"is lower than that of the {}".format(self))
# Interior product at the component level:
basis = self.common_basis(alt_tensor)
if basis is None:
raise ValueError("no common basis for the interior product")
comp = self._components[basis].interior_product(
alt_tensor._components[basis])
if p_res == 0:
res = comp # result is a scalar
else:
res = self._fmodule.tensor_from_comp((p_res, 0), comp)
# Name of the result
res_name = None
if self._name is not None and alt_tensor._name is not None:
sname = self._name
oname = alt_tensor._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
res_name = 'i_' + sname + ' ' + oname
res_latex_name = None
if self._latex_name is not None and alt_tensor._latex_name is not None:
slname = self._latex_name
olname = alt_tensor._latex_name
if not is_atomic(olname):
olname = r'\left(' + olname + r'\right)'
res_latex_name = r'\iota_{' + slname + '} ' + olname
if p_res == 0:
if res_name:
try: # there is no guarantee that base ring elements have
# set_name
res.set_name(res_name, latex_name=res_latex_name)
except (AttributeError, TypeError):
pass
else:
res.set_name(res_name, latex_name=res_latex_name)
return res
def wedge(self, other):
r"""
Exterior product with another differential form.
INPUT:
- ``other``: another differential form
OUTPUT:
- instance of :class:`DiffForm` representing the exterior
product self/\\other.
"""
from sage.tensor.modules.free_module_alt_form import FreeModuleAltForm
from sage.tensor.modules.format_utilities import is_atomic
if self._domain.is_subset(other._domain):
if not self._ambient_domain.is_subset(other._ambient_domain):
raise TypeError("Incompatible ambient domains for exterior " +
"product.")
elif other._domain.is_subset(self._domain):
if not other._ambient_domain.is_subset(self._ambient_domain):
raise TypeError("Incompatible ambient domains for exterior " +
"product.")
dom_resu = self._domain.intersection(other._domain)
ambient_dom_resu = self._ambient_domain.intersection(
other._ambient_domain)
self_r = self.restrict(dom_resu)
other_r = other.restrict(dom_resu)
if ambient_dom_resu.is_manifestly_parallelizable():
# call of the FreeModuleAltForm version:
return FreeModuleAltForm.wedge(self_r, other_r)
# otherwise, the result is created here:
if self._name is not None and other._name is not None:
sname = self._name
oname = other._name
if not is_atomic(sname):
sname = '(' + sname + ')'
if not is_atomic(oname):
oname = '(' + oname + ')'
resu_name = sname + '/\\' + oname
if self._latex_name is not None and other._latex_name is not None:
slname = self._latex_name
olname = other._latex_name
if not is_atomic(slname):
slname = '(' + slname + ')'
if not is_atomic(olname):
olname = '(' + olname + ')'
resu_latex_name = slname + r'\wedge ' + olname
dest_map = self._vmodule._dest_map
dest_map_resu = dest_map.restrict(dom_resu,
subcodomain=ambient_dom_resu)
vmodule = dom_resu.vector_field_module(dest_map=dest_map_resu)
resu_degree = self._tensor_rank + other._tensor_rank
resu = vmodule.alternating_form(resu_degree,
name=resu_name,
latex_name=resu_latex_name)
for dom in self_r._restrictions:
if dom in other_r._restrictions:
resu._restrictions[dom] = self_r._restrictions[dom].wedge(
other_r._restrictions[dom])
return resu
def _display_expansion(self, basis=None, format_spec=None):
r"""
Return the pure expansion of ``self`` w.r.t. a given module basis.
The expansion is actually performed onto exterior products of elements
of the cobasis (dual basis) associated with ``basis`` (see examples
below). The output is either text-formatted (console mode) or
LaTeX-formatted (notebook mode).
INPUT:
- ``basis`` -- (default: ``None``) basis of the free module with
respect to which the alternating form is expanded; if none is
provided, the module's default basis is assumed
- ``format_spec`` -- (default: ``None``) format specification passed
to ``self._fmodule._output_formatter`` to format the output
TESTS:
Expansion display of an alternating form of degree 1 (linear form) on a
rank-3 free module::
sage: M = FiniteRankFreeModule(ZZ, 3, name='M')
sage: e = M.basis('e')
sage: e.dual_basis()
Dual basis (e^0,e^1,e^2) on the Rank-3 free module M over the Integer Ring
sage: a = M.linear_form('a', latex_name=r'\alpha')
sage: a[:] = [1,-3,4]
sage: a._display_expansion(e)
e^0 - 3 e^1 + 4 e^2
sage: a._display_expansion() # a shortcut since e is M's default basis
e^0 - 3 e^1 + 4 e^2
sage: latex(a._display_expansion()) # display in the notebook
e^{0} -3 e^{1} + 4 e^{2}
"""
from sage.misc.latex import latex
from sage.tensor.modules.format_utilities import (is_atomic,
FormattedExpansion)
basis, format_spec = self._preparse_display(basis=basis,
format_spec=format_spec)
cobasis = basis.dual_basis()
comp = self.comp(basis)
terms_txt = []
terms_latex = []
for ind in comp.non_redundant_index_generator():
ind_arg = ind + (format_spec, )
coef = comp[ind_arg]
# Check whether the coefficient is zero, preferably via
# the fast method is_trivial_zero():
if hasattr(coef, 'is_trivial_zero'):
zero_coef = coef.is_trivial_zero()
else:
zero_coef = coef == 0
if not zero_coef:
bases_txt = []
bases_latex = []
for k in range(self._tensor_rank):
bases_txt.append(cobasis[ind[k]]._name)
bases_latex.append(latex(cobasis[ind[k]]))
basis_term_txt = "/\\".join(bases_txt)
basis_term_latex = r"\wedge ".join(bases_latex)
coef_txt = repr(coef)
if coef_txt == "1":
terms_txt.append(basis_term_txt)
terms_latex.append(basis_term_latex)
elif coef_txt == "-1":
terms_txt.append("-" + basis_term_txt)
terms_latex.append("-" + basis_term_latex)
else:
coef_latex = latex(coef)
if is_atomic(coef_txt):
terms_txt.append(coef_txt + " " + basis_term_txt)
else:
terms_txt.append("(" + coef_txt + ") " +
basis_term_txt)
if is_atomic(coef_latex):
terms_latex.append(coef_latex + basis_term_latex)
else:
terms_latex.append(r"\left(" + coef_latex + \
r"\right)" + basis_term_latex)
if not terms_txt:
expansion_txt = "0"
else:
expansion_txt = terms_txt[0]
for term in terms_txt[1:]:
if term[0] == "-":
expansion_txt += " - " + term[1:]
else:
expansion_txt += " + " + term
if not terms_latex:
expansion_latex = "0"
else:
expansion_latex = terms_latex[0]
for term in terms_latex[1:]:
if term[0] == "-":
expansion_latex += term
else:
expansion_latex += "+" + term
return FormattedExpansion(expansion_txt, expansion_latex)