"""
Free modules
"""
from sage.structure.unique_representation import UniqueRepresentation
from sage.structure.element import Element
from sage.structure.parent import Parent
from sage.structure.sage_object import have_same_parent
from sage.modules.free_module_element import vector
from sage.misc.misc import repr_lincomb
from sage.modules.module import Module
from sage.rings.all import Integer
import sage.structure.element
from sage.combinat.family import Family
from sage.sets.finite_enumerated_set import FiniteEnumeratedSet
from sage.combinat.cartesian_product import CartesianProduct
from sage.sets.disjoint_union_enumerated_sets import DisjointUnionEnumeratedSets
from sage.misc.cachefunc import cached_method
from sage.misc.all import lazy_attribute
from sage.categories.poor_man_map import PoorManMap
from sage.categories.all import ModulesWithBasis
from sage.combinat.dict_addition import dict_addition, dict_linear_combination
class CombinatorialFreeModuleElement(Element):
def __init__(self, M, x):
"""
Create a combinatorial module element. This should never be
called directly, but only through the parent combinatorial
free module's :meth:`__call__` method.
TESTS::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 3*B['c']; f
B['a'] + 3*B['c']
sage: f == loads(dumps(f))
True
"""
Element.__init__(self, M)
self._monomial_coefficients = x
def __iter__(self):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 3*B['c']
sage: [i for i in sorted(f)]
[('a', 1), ('c', 3)]
::
sage: s = SFASchur(QQ)
sage: a = s([2,1]) + s([3])
sage: [i for i in sorted(a)]
[([2, 1], 1), ([3], 1)]
"""
return self._monomial_coefficients.iteritems()
def __contains__(self, x):
"""
Returns whether or not a combinatorial object x indexing a basis
element is in the support of self.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 3*B['c']
sage: 'a' in f
True
sage: 'b' in f
False
::
sage: s = SFASchur(QQ)
sage: a = s([2,1]) + s([3])
sage: Partition([2,1]) in a
True
sage: Partition([1,1,1]) in a
False
"""
return x in self._monomial_coefficients and self._monomial_coefficients[x] != 0
def monomial_coefficients(self):
"""
Return the internal dictionary which has the combinatorial objects
indexing the basis as keys and their corresponding coefficients as
values.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 3*B['c']
sage: d = f.monomial_coefficients()
sage: d['a']
1
sage: d['c']
3
To run through the monomials of an element, it is better to
use the idiom::
sage: for (t,c) in f:
... print t,c
a 1
c 3
::
sage: s = SFASchur(QQ)
sage: a = s([2,1])+2*s([3,2])
sage: d = a.monomial_coefficients()
sage: type(d)
<type 'dict'>
sage: d[ Partition([2,1]) ]
1
sage: d[ Partition([3,2]) ]
2
"""
return self._monomial_coefficients
def _sorted_items_for_printing(self):
"""
Returns the items (i.e terms) of ``self``, sorted for printing
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 2*B['c'] + 3 * B['b']
sage: f._sorted_items_for_printing()
[('a', 1), ('b', 3), ('c', 2)]
sage: F.print_options(monomial_cmp = lambda x,y: -cmp(x,y))
sage: f._sorted_items_for_printing()
[('c', 2), ('b', 3), ('a', 1)]
.. seealso:: :meth:`_repr_`, :meth:`_latex_`, :meth:`print_options`
"""
print_options = self.parent().print_options()
v = self._monomial_coefficients.items()
try:
v.sort(cmp = print_options['monomial_cmp'],
key = lambda (monomial,coeff): monomial)
except StandardError:
pass
return v
def _repr_(self):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'], prefix='F')
sage: e = F.basis()
sage: e['a'] + 2*e['b'] # indirect doctest
F['a'] + 2*F['b']
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'], prefix='')
sage: e = F.basis()
sage: e['a'] + 2*e['b'] # indirect doctest
['a'] + 2*['b']
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'], prefix='', scalar_mult=' ', bracket=False)
sage: e = F.basis()
sage: e['a'] + 2*e['b'] # indirect doctest
'a' + 2 'b'
Controling the order of terms by providing a comparison
function on elements of the support::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'],
... monomial_cmp = lambda x,y: cmp(y,x))
sage: e = F.basis()
sage: e['a'] + 3*e['b'] + 2*e['c']
2*B['c'] + 3*B['b'] + B['a']
sage: F = CombinatorialFreeModule(QQ, ['ac', 'ba', 'cb'],
... monomial_cmp = lambda x,y: cmp(x[1],y[1]))
sage: e = F.basis()
sage: e['ac'] + 3*e['ba'] + 2*e['cb']
3*B['ba'] + 2*B['cb'] + B['ac']
"""
return repr_lincomb(self._sorted_items_for_printing(),
scalar_mult=self.parent()._print_options['scalar_mult'],
repr_monomial = self.parent()._repr_term,
strip_one = True)
def _latex_(self):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 3*B['c']
sage: latex(f)
B_{a} + 3B_{c}
::
sage: QS3 = SymmetricGroupAlgebra(QQ,3)
sage: a = 2 + QS3([2,1,3])
sage: latex(a) #indirect doctest
2[1, 2, 3] + [2, 1, 3]
::
sage: F = CombinatorialFreeModule(QQ, ['a','b'], prefix='beta', latex_prefix='\\beta')
sage: x = F.an_element()
sage: x
2*beta['a'] + 2*beta['b']
sage: latex(x)
2\beta_{a} + 2\beta_{b}
Controling the order of terms by providing a comparison
function on elements of the support::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'],
... monomial_cmp = lambda x,y: cmp(y,x))
sage: e = F.basis()
sage: latex(e['a'] + 3*e['b'] + 2*e['c'])
2B_{c} + 3B_{b} + B_{a}
sage: F = CombinatorialFreeModule(QQ, ['ac', 'ba', 'cb'],
... monomial_cmp = lambda x,y: cmp(x[1],y[1]))
sage: e = F.basis()
sage: latex(e['ac'] + 3*e['ba'] + 2*e['cb'])
3B_{ba} + 2B_{cb} + B_{ac}
"""
return repr_lincomb(self._sorted_items_for_printing(),
scalar_mult = self.parent()._print_options['scalar_mult'],
latex_scalar_mult = self.parent()._print_options['latex_scalar_mult'],
repr_monomial = self.parent()._latex_term,
is_latex=True, strip_one = True)
def __eq__(self, other):
"""
EXAMPLES::
sage: F1 = CombinatorialFreeModule(QQ, [1, 2, 3])
sage: F2 = CombinatorialFreeModule(QQ, [1, 2, 3], prefix = "g")
sage: F1.zero() == F1.zero()
True
sage: F1.zero() == F1.an_element()
False
sage: F1.an_element() == F1.an_element()
True
Currently, if ``self`` and ``other`` do not have the same
parent, coercions are attempted::
sage: F1.zero() == 0
True
sage: F1.zero() == F2.zero()
False
sage: F1.an_element() == None
False
sage: F = AlgebrasWithBasis(QQ).example()
sage: F.one() == 1
True
sage: 1 == F.one()
True
sage: 2 * F.one() == int(2)
True
sage: int(2) == 2 * F.one()
True
sage: S = SymmetricFunctions(QQ); s = S.s(); p = S.p()
sage: p[2] == s[2] - s[1, 1]
True
sage: p[2] == s[2]
False
This feature is disputable, in particular since it can make
equality testing costly. It may be removed at some point.
Equality testing can be a bit tricky when the order of terms
can vary because their indices are incomparable with
``cmp``. The following test did fail before :trac:`12489` ::
sage: F = CombinatorialFreeModule(QQ, Subsets([1,2,3]))
sage: x = F.an_element()
sage: (x+F.zero()).terms() # random
[2*B[{1}], 3*B[{2}], B[{}]]
sage: x.terms() # random
[2*B[{1}], B[{}], 3*B[{2}]]
sage: x+F.zero() == x
True
TESTS::
sage: TestSuite(F1).run()
sage: TestSuite(F).run()
"""
if have_same_parent(self, other):
return self._monomial_coefficients == other._monomial_coefficients
from sage.structure.element import get_coercion_model
import operator
try:
return get_coercion_model().bin_op(self, other, operator.eq)
except TypeError:
return False
def __ne__(left, right):
"""
EXAMPLES::
sage: F1 = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: F1.an_element() != F1.an_element()
False
sage: F1.an_element() != F1.zero()
True
"""
return not left == right
def __cmp__(left, right):
"""
The ordering is the one on the underlying sorted list of
(monomial,coefficients) pairs.
EXAMPLES::
sage: s = SFASchur(QQ)
sage: a = s([2,1])
sage: b = s([1,1,1])
sage: cmp(a,b) #indirect doctest
1
"""
if have_same_parent(left, right) and left._monomial_coefficients == right._monomial_coefficients:
return 0
nonzero = lambda mc: mc[1] != 0
v = filter(nonzero, left._monomial_coefficients.items())
v.sort()
w = filter(nonzero, right._monomial_coefficients.items())
w.sort()
return cmp(v, w)
def _add_(self, other):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: B['a'] + 3*B['c']
B['a'] + 3*B['c']
::
sage: s = SFASchur(QQ)
sage: s([2,1]) + s([5,4]) # indirect doctest
s[2, 1] + s[5, 4]
sage: a = s([2,1]) + 0
sage: len(a.monomial_coefficients())
1
"""
assert hasattr( other, 'parent' ) and other.parent() == self.parent()
F = self.parent()
return F._from_dict( dict_addition( [ self._monomial_coefficients, other._monomial_coefficients ] ), remove_zeros=False )
def _neg_(self):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 3*B['c']
sage: -f
-B['a'] - 3*B['c']
::
sage: s = SFASchur(QQ)
sage: -s([2,1]) # indirect doctest
-s[2, 1]
"""
F = self.parent()
return F._from_dict( dict_linear_combination( [ ( self._monomial_coefficients, -1 ) ] ), remove_zeros=False )
def _sub_(self, other):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: B['a'] - 3*B['c']
B['a'] - 3*B['c']
::
sage: s = SFASchur(QQ)
sage: s([2,1]) - s([5,4]) # indirect doctest
s[2, 1] - s[5, 4]
"""
assert hasattr( other, 'parent' ) and other.parent() == self.parent()
F = self.parent()
return F._from_dict( dict_linear_combination( [ ( self._monomial_coefficients, 1 ), (other._monomial_coefficients, -1 ) ] ), remove_zeros=False )
def _coefficient_fast(self, m, default=None):
"""
Returns the coefficient of m in self, where m is key in
self._monomial_coefficients.
EXAMPLES::
sage: p = Partition([2,1])
sage: q = Partition([1,1,1])
sage: s = SFASchur(QQ)
sage: a = s(p)
sage: a._coefficient_fast([2,1])
Traceback (most recent call last):
...
TypeError: unhashable type: 'list'
::
sage: a._coefficient_fast(p)
1
sage: a._coefficient_fast(p, 2)
1
sage: a._coefficient_fast(q)
0
sage: a._coefficient_fast(q, 2)
2
sage: a[p]
1
sage: a[q]
0
"""
if default is None:
default = self.base_ring()(0)
return self._monomial_coefficients.get(m, default)
__getitem__ = _coefficient_fast
def coefficient(self, m):
"""
EXAMPLES::
sage: s = CombinatorialFreeModule(QQ, Partitions())
sage: z = s([4]) - 2*s([2,1]) + s([1,1,1]) + s([1])
sage: z.coefficient([4])
1
sage: z.coefficient([2,1])
-2
sage: z.coefficient(Partition([2,1]))
-2
sage: z.coefficient([1,2])
Traceback (most recent call last):
...
AssertionError: [1, 2] should be an element of Partitions
sage: z.coefficient(Composition([2,1]))
Traceback (most recent call last):
...
AssertionError: [2, 1] should be an element of Partitions
Test that coefficient also works for those parents that do not yet have an element_class::
sage: G = DihedralGroup(3)
sage: F = CombinatorialFreeModule(QQ, G)
sage: hasattr(G, "element_class")
False
sage: g = G.an_element()
sage: (2*F.monomial(g)).coefficient(g)
2
"""
C = self.parent()._basis_keys
assert m in C, "%s should be an element of %s"%(m, C)
if hasattr(C, "element_class") and not isinstance(m, C.element_class):
m = C(m)
return self._coefficient_fast(m)
def is_zero(self):
"""
Returns True if and only self == 0.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] - 3*B['c']
sage: f.is_zero()
False
sage: F.zero().is_zero()
True
::
sage: s = SFASchur(QQ)
sage: s([2,1]).is_zero()
False
sage: s(0).is_zero()
True
sage: (s([2,1]) - s([2,1])).is_zero()
True
"""
BR = self.parent().base_ring()
zero = BR( 0 )
return all( v == zero for v in self._monomial_coefficients.values() )
def __len__(self):
"""
Returns the number of basis elements of self with nonzero
coefficients.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] - 3*B['c']
sage: len(f)
2
::
sage: s = SFASchur(QQ)
sage: z = s([4]) + s([2,1]) + s([1,1,1]) + s([1])
sage: len(z)
4
"""
return self.length()
def length(self):
"""
Returns the number of basis elements of self with nonzero
coefficients.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] - 3*B['c']
sage: f.length()
2
::
sage: s = SFASchur(QQ)
sage: z = s([4]) + s([2,1]) + s([1,1,1]) + s([1])
sage: z.length()
4
"""
BR = self.parent().base_ring()
zero = BR( 0 )
return len( [ key for key, coeff in self._monomial_coefficients.iteritems() if coeff != zero ] )
def support(self):
"""
Returns a list of the combinatorial objects indexing the basis
elements of self which non-zero coefficients.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] - 3*B['c']
sage: f.support()
['a', 'c']
::
sage: s = SFASchur(QQ)
sage: z = s([4]) + s([2,1]) + s([1,1,1]) + s([1])
sage: z.support()
[[1], [1, 1, 1], [2, 1], [4]]
"""
BR = self.parent().base_ring()
zero = BR( 0 )
supp = [ key for key, coeff in self._monomial_coefficients.iteritems() if coeff != zero ]
supp.sort()
return supp
def monomials(self):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 2*B['c']
sage: f.monomials()
[B['a'], B['c']]
"""
P = self.parent()
BR = P.base_ring()
zero = BR( 0 )
one = BR( 1 )
supp = [ key for key, coeff in self._monomial_coefficients.iteritems() if coeff != zero ]
supp.sort()
return [ P._from_dict( { key : one }, remove_zeros=False ) for key in supp ]
def terms(self):
"""
Returns a list of the terms of ``self``
.. seealso:: :meth:`monomials`
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] + 2*B['c']
sage: f.terms()
[B['a'], 2*B['c']]
"""
BR = self.parent().base_ring()
zero = BR( 0 )
v = [ ( key, value ) for key, value in self._monomial_coefficients.iteritems() if value != zero ]
v.sort()
from_dict = self.parent()._from_dict
return [ from_dict( { key : value } ) for key,value in v ]
def coefficients(self):
"""
Returns a list of the coefficients appearing on the basis elements in
self.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] - 3*B['c']
sage: f.coefficients()
[1, -3]
::
sage: s = SFASchur(QQ)
sage: z = s([4]) + s([2,1]) + s([1,1,1]) + s([1])
sage: z.coefficients()
[1, 1, 1, 1]
"""
BR = self.parent().base_ring()
zero = BR( 0 )
v = [ ( key, value ) for key, value in self._monomial_coefficients.iteritems() if value != zero ]
v.sort()
return [ value for key,value in v ]
def _vector_(self, new_base_ring=None):
"""
Returns a vector version of self. If ''new_base_ring'' is specified,
then in returns a vector over ''new_base_ring''.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] - 3*B['c']
sage: vector(f)
(1, 0, -3)
::
sage: QS3 = SymmetricGroupAlgebra(QQ, 3)
sage: a = 2*QS3([1,2,3])+4*QS3([3,2,1])
sage: a._vector_()
(2, 0, 0, 0, 0, 4)
sage: vector(a)
(2, 0, 0, 0, 0, 4)
sage: a._vector_(RDF)
(2.0, 0.0, 0.0, 0.0, 0.0, 4.0)
"""
parent = self.parent()
cc = parent.get_order()
if new_base_ring is None:
new_base_ring = parent.base_ring()
return vector(new_base_ring,
[new_base_ring(self._monomial_coefficients.get(m, 0))
for m in list(cc)])
def to_vector(self):
"""
Returns a vector version of self.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: f = B['a'] - 3*B['c']
sage: f.to_vector()
(1, 0, -3)
::
sage: QS3 = SymmetricGroupAlgebra(QQ, 3)
sage: a = 2*QS3([1,2,3])+4*QS3([3,2,1])
sage: a.to_vector()
(2, 0, 0, 0, 0, 4)
sage: a == QS3.from_vector(a.to_vector())
True
"""
return self._vector_()
def _acted_upon_(self, scalar, self_on_left = False):
"""
Returns the action of a scalar on self
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: B = F.basis()
sage: B['a']*(1/2) # indirect doctest
1/2*B['a']
sage: B['a']/2
1/2*B['a']
sage: B['a']*2 # indirect doctest
2*B['a']
sage: B['a']*int(2) # indirect doctest
2*B['a']
sage: 1/2*B['a']
1/2*B['a']
sage: 2*B['a'] # indirect doctest
2*B['a']
sage: int(2)*B['a'] # indirect doctest
2*B['a']
TESTS::
sage: F.get_action(QQ, operator.mul, True)
Right action by Rational Field on Free module generated by {'a', 'b', 'c'} over Rational Field
sage: F.get_action(QQ, operator.mul, False)
Left action by Rational Field on Free module generated by {'a', 'b', 'c'} over Rational Field
sage: F.get_action(ZZ, operator.mul, True)
Right action by Integer Ring on Free module generated by {'a', 'b', 'c'} over Rational Field
sage: F.get_action(F, operator.mul, True)
sage: F.get_action(F, operator.mul, False)
This also works when a coercion of the coefficient is needed, for
example with polynomials or fraction fields #8832::
sage: P.<q> = QQ['q']
sage: V = CombinatorialFreeModule(P, Permutations())
sage: el = V(Permutation([3,1,2]))
sage: (3/2)*el
3/2*B[[3, 1, 2]]
sage: P.<q> = QQ['q']
sage: F = FractionField(P)
sage: V = CombinatorialFreeModule(F, Words())
sage: w = Words()('abc')
sage: (1+q)*V(w)
(q+1)*B[word: abc]
sage: ((1+q)/q)*V(w)
((q+1)/q)*B[word: abc]
TODO:
- add non commutative tests
"""
if hasattr( scalar, 'parent' ) and scalar.parent() != self.base_ring():
if self.base_ring().has_coerce_map_from(scalar.parent()):
scalar = self.base_ring()( scalar )
else:
return None
F = self.parent()
D = self._monomial_coefficients
if self_on_left:
D = dict_linear_combination( [ ( D, scalar ) ], factor_on_left = False )
else:
D = dict_linear_combination( [ ( D, scalar ) ] )
return F._from_dict( D, remove_zeros=False )
_lmul_ = _acted_upon_
_rmul_ = _acted_upon_
def __div__(self, x, self_on_left=False ):
"""
Division by coefficients
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, [1,2,3])
sage: x = F._from_dict({1:2, 2:3})
sage: x/2
B[1] + 3/2*B[2]
::
sage: F = CombinatorialFreeModule(QQ, [1,2,3])
sage: B = F.basis()
sage: f = 2*B[2] + 4*B[3]
sage: f/2
B[2] + 2*B[3]
"""
if self.base_ring().is_field():
F = self.parent()
x = self.base_ring()( x )
x_inv = x**-1
D = self._monomial_coefficients
if self_on_left:
D = dict_linear_combination( [ ( D, x_inv ) ], factor_on_left=False )
else:
D = dict_linear_combination( [ ( D, x_inv ) ] )
return F._from_dict( D, remove_zeros=False )
else:
return self.map_coefficients(lambda c: _divide_if_possible(c, x))
def _divide_if_possible(x, y):
"""
EXAMPLES::
sage: from sage.combinat.free_module import _divide_if_possible
sage: _divide_if_possible(4, 2)
2
sage: _.parent()
Integer Ring
::
sage: _divide_if_possible(4, 3)
Traceback (most recent call last):
...
ValueError: 4 is not divisible by 3
"""
q, r = x.quo_rem(y)
if r != 0:
raise ValueError, "%s is not divisible by %s"%(x, y)
else:
return q
class CombinatorialFreeModule(UniqueRepresentation, Module):
r"""
Class for free modules with a named basis
INPUT:
- ``R`` - base ring
- ``basis_keys`` - list, tuple, family, set, etc. defining the
indexing set for the basis of this module
- ``element_class`` - the class of which elements of this module
should be instances (optional, default None, in which case the
elements are instances of
:class:`CombinatorialFreeModuleElement`)
- ``category`` - the category in which this module lies (optional,
default None, in which case use the "category of modules with
basis" over the base ring ``R``)
Options controlling the printing of elements:
- ``prefix`` - string, prefix used for printing elements of this
module (optional, default 'B'). With the default, a monomial
indexed by 'a' would be printed as ``B['a']``.
- ``latex_prefix`` - string or None, prefix used in the LaTeX
representation of elements (optional, default None). If this is
anything except the empty string, it prints the index as a
subscript. If this is None, it uses the setting for ``prefix``,
so if ``prefix`` is set to "B", then a monomial indexed by 'a'
would be printed as ``B_{a}``. If this is the empty string, then
don't print monomials as subscripts: the monomial indexed by 'a'
would be printed as ``a``, or as ``[a]`` if ``latex_bracket`` is
True.
- ``bracket`` - None, bool, string, or list or tuple of
strings (optional, default None): if None, use the value of the
attribute ``self._repr_option_bracket``, which has default value
True. (``self._repr_option_bracket`` is available for backwards
compatibility. Users should set ``bracket`` instead. If
``bracket`` is set to anything except None, it overrides
the value of ``self._repr_option_bracket``.) If False, do not
include brackets when printing elements: a monomial indexed by
'a' would be printed as ``B'a'``, and a monomial indexed by
(1,2,3) would be printed as ``B(1,2,3)``. If True, use "[" and
"]" as brackets. If it is one of "[", "(", or "{", use it and
its partner as brackets. If it is any other string, use it as
both brackets. If it is a list or tuple of strings, use the
first entry as the left bracket and the second entry as the
right bracket.
- ``latex_bracket`` - bool, string, or list or tuple of strings
(optional, default False): if False, do not include brackets in
the LaTeX representation of elements. This option is only
relevant if ``latex_prefix`` is the empty string; otherwise,
brackets are not used regardless. If True, use "\\left[" and
"\\right]" as brackets. If this is one of "[", "(", "\\{", "|",
or "||", use it and its partner, prepended with "\\left" and
"\\right", as brackets. If this is any other string, use it as
both brackets. If this is a list or tuple of strings, use the
first entry as the left bracket and the second entry as the
right bracket.
- ``scalar_mult`` - string to use for scalar multiplication in
the print representation (optional, default "*")
- ``latex_scalar_mult`` - string or None (optional, default None),
string to use for scalar multiplication in the latex
representation. If None, use the empty string if ``scalar_mult``
is set to "*", otherwise use the value of ``scalar_mult``.
- ``tensor_symbol`` - string or None (optional, default None),
string to use for tensor product in the print representation. If
None, use the ``sage.categories.tensor.symbol``.
- ``monomial_cmp`` - a comparison function (optional, default cmp),
to use for sorting elements in the output of elements
.. note:: These print options may also be accessed and modified using the
:meth:`print_options` method, after the module has been defined.
EXAMPLES:
We construct a free module whose basis is indexed by the letters a, b, c::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: F
Free module generated by {'a', 'b', 'c'} over Rational Field
Its basis is a family, indexed by a, b, c::
sage: e = F.basis()
sage: e
Finite family {'a': B['a'], 'c': B['c'], 'b': B['b']}
::
sage: [x for x in e]
[B['a'], B['b'], B['c']]
sage: [k for k in e.keys()]
['a', 'b', 'c']
Let us construct some elements, and compute with them::
sage: e['a']
B['a']
sage: 2*e['a']
2*B['a']
sage: e['a'] + 3*e['b']
B['a'] + 3*B['b']
Some uses of
:meth:`sage.categories.commutative_additive_semigroups.CommutativeAdditiveSemigroups.ParentMethods.summation`
and :meth:`.sum`::
sage: F = CombinatorialFreeModule(QQ, [1,2,3,4])
sage: F.summation(F.monomial(1), F.monomial(3))
B[1] + B[3]
sage: F = CombinatorialFreeModule(QQ, [1,2,3,4])
sage: F.sum(F.monomial(i) for i in [1,2,3])
B[1] + B[2] + B[3]
Note that free modules with a given basis and parameters are unique::
sage: F1 = CombinatorialFreeModule(QQ, (1,2,3,4))
sage: F1 is F
True
The constructed free module depends on the order of the basis and
on the other parameters, like the prefix::
sage: F1 = CombinatorialFreeModule(QQ, (1,2,3,4))
sage: F1 is F
True
sage: F1 = CombinatorialFreeModule(QQ, [4,3,2,1])
sage: F1 == F
False
sage: F2 = CombinatorialFreeModule(QQ, [1,2,3,4], prefix='F')
sage: F2 == F
False
Because of this, if you create a free module with certain
parameters and then modify its prefix or other print options, this
affects all modules which were defined using the same parameters::
sage: F2.print_options(prefix='x')
sage: F2.prefix()
'x'
sage: F3 = CombinatorialFreeModule(QQ, [1,2,3,4], prefix='F')
sage: F3 is F2 # F3 was defined just like F2
True
sage: F3.prefix()
'x'
sage: F4 = CombinatorialFreeModule(QQ, [1,2,3,4], prefix='F', bracket=True)
sage: F4 == F2 # F4 was NOT defined just like F2
False
sage: F4.prefix()
'F'
The default category is the category of modules with basis over
the base ring::
sage: CombinatorialFreeModule(GF(3), ((1,2), (3,4))).category()
Category of modules with basis over Finite Field of size 3
See :mod:`sage.categories.examples.algebras_with_basis` and
:mod:`sage.categories.examples.hopf_algebras_with_basis` for
illustrations of the use of the ``category`` keyword, and see
:class:`sage.combinat.root_system.weight_space.WeightSpace` for an
example of the use of ``element_class``.
Customizing print and LaTeX representations of elements::
sage: F = CombinatorialFreeModule(QQ, ['a','b'], prefix='x')
sage: e = F.basis()
sage: e['a'] - 3 * e['b']
x['a'] - 3*x['b']
sage: F.print_options(prefix='x', scalar_mult=' ', bracket='{')
sage: e['a'] - 3 * e['b']
x{'a'} - 3 x{'b'}
sage: latex(e['a'] - 3 * e['b'])
x_{a} + \left(-3\right) x_{b}
sage: F.print_options(latex_prefix='y')
sage: latex(e['a'] - 3 * e['b'])
y_{a} + \left(-3\right) y_{b}
sage: F.print_options(monomial_cmp = lambda x,y: -cmp(x,y))
sage: e['a'] - 3 * e['b']
-3 x{'b'} + x{'a'}
sage: F = CombinatorialFreeModule(QQ, [(1,2), (3,4)])
sage: e = F.basis()
sage: e[(1,2)] - 3 * e[(3,4)]
B[(1, 2)] - 3*B[(3, 4)]
sage: F.print_options(bracket=['_{', '}'])
sage: e[(1,2)] - 3 * e[(3,4)]
B_{(1, 2)} - 3*B_{(3, 4)}
sage: F.print_options(prefix='', bracket=False)
sage: e[(1,2)] - 3 * e[(3,4)]
(1, 2) - 3*(3, 4)
"""
@staticmethod
def __classcall_private__(cls, base_ring, basis_keys, category = None, **keywords):
"""
TESTS::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: G = CombinatorialFreeModule(QQ, ('a','b','c'))
sage: F is G
True
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'], latex_bracket=['LEFT', 'RIGHT'])
sage: F.print_options()['latex_bracket']
('LEFT', 'RIGHT')
sage: F is G
False
We check that the category is properly straightened::
sage: F = CombinatorialFreeModule(QQ, ['a','b'])
sage: F1 = CombinatorialFreeModule(QQ, ['a','b'], category = ModulesWithBasis(QQ))
sage: F2 = CombinatorialFreeModule(QQ, ['a','b'], category = [ModulesWithBasis(QQ)])
sage: F3 = CombinatorialFreeModule(QQ, ['a','b'], category = (ModulesWithBasis(QQ),))
sage: F4 = CombinatorialFreeModule(QQ, ['a','b'], category = (ModulesWithBasis(QQ),CommutativeAdditiveSemigroups()))
sage: F5 = CombinatorialFreeModule(QQ, ['a','b'], category = (ModulesWithBasis(QQ),Category.join((LeftModules(QQ), RightModules(QQ)))))
sage: F1 is F, F2 is F, F3 is F, F4 is F, F5 is F
(True, True, True, True, True)
sage: G = CombinatorialFreeModule(QQ, ['a','b'], category = AlgebrasWithBasis(QQ))
sage: F is G
False
"""
if isinstance(basis_keys, (list, tuple)):
basis_keys = FiniteEnumeratedSet(basis_keys)
category = ModulesWithBasis(base_ring).or_subcategory(category)
bracket = keywords.get('bracket', None)
if isinstance(bracket, list):
keywords['bracket'] = tuple(bracket)
latex_bracket = keywords.get('latex_bracket', None)
if isinstance(latex_bracket, list):
keywords['latex_bracket'] = tuple(latex_bracket)
return super(CombinatorialFreeModule, cls).__classcall__(cls, base_ring, basis_keys, category = category, **keywords)
Element = CombinatorialFreeModuleElement
def __init__(self, R, basis_keys, element_class = None, category = None, **kwds):
r"""
TESTS::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: F.category()
Category of modules with basis over Rational Field
One may specify the category this module belongs to::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'], category=AlgebrasWithBasis(QQ))
sage: F.category()
Category of algebras with basis over Rational Field
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'], category = FiniteDimensionalModulesWithBasis(QQ))
sage: F.basis()
Finite family {'a': B['a'], 'c': B['c'], 'b': B['b']}
sage: F.category()
Category of finite dimensional modules with basis over Rational Field
sage: TestSuite(F).run()
TESTS:
Regression test for #10127: ``self._basis_keys`` needs to be
set early enough, in case the initialization of the categories
use ``self.basis().keys()``. This occured on several occasions
in non trivial constructions. In the following example,
:class:`AlgebrasWithBasis` constructs ``Homset(self,self)`` to
extend by bilinearity method ``product_on_basis``, which in
turn triggers ``self._repr_()``::
sage: class MyAlgebra(CombinatorialFreeModule):
... def _repr_(self):
... return "MyAlgebra on %s"%(self.basis().keys())
... def product_on_basis(self,i,j):
... pass
sage: MyAlgebra(ZZ, ZZ, category = AlgebrasWithBasis(QQ))
MyAlgebra on Integer Ring
A simpler example would be welcome!
We check that unknown options are caught::
sage: CombinatorialFreeModule(ZZ, [1,2,3], keyy=2)
Traceback (most recent call last):
...
ValueError: keyy is not a valid print option.
"""
from sage.categories.all import Rings
if R not in Rings():
raise TypeError, "Argument R must be a ring."
if category is None:
category = ModulesWithBasis(R)
if element_class is not None:
self.Element = element_class
if isinstance(basis_keys, (list, tuple)):
basis_keys = FiniteEnumeratedSet(basis_keys)
if not hasattr(self, "_name"):
self._name = "Free module generated by %s"%(basis_keys,)
self._basis_keys = basis_keys
Parent.__init__(self, base = R, category = category,
element_constructor = self._element_constructor_)
self._order = None
self._print_options = {'prefix': "B",
'bracket': None,
'latex_bracket': False,
'latex_prefix': None,
'scalar_mult': "*",
'latex_scalar_mult': None,
'tensor_symbol': None,
'monomial_cmp': cmp}
kwds.pop('key', None)
self.print_options(**kwds)
@lazy_attribute
def _element_class(self):
"""
TESTS::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: F._element_class
<class 'sage.combinat.free_module.CombinatorialFreeModule_with_category.element_class'>
"""
return self.element_class
@cached_method
def basis(self):
"""
Returns the basis of self.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a','b','c'])
sage: F.basis()
Finite family {'a': B['a'], 'c': B['c'], 'b': B['b']}
::
sage: QS3 = SymmetricGroupAlgebra(QQ,3)
sage: list(QS3.basis())
[[1, 2, 3], [1, 3, 2], [2, 1, 3], [2, 3, 1], [3, 1, 2], [3, 2, 1]]
"""
return Family(self._basis_keys, self.monomial)
def _an_element_(self):
"""
EXAMPLES::
sage: CombinatorialFreeModule(QQ, ("a", "b", "c")).an_element()
2*B['a'] + 2*B['b'] + 3*B['c']
sage: CombinatorialFreeModule(QQ, ("a", "b", "c"))._an_element_()
2*B['a'] + 2*B['b'] + 3*B['c']
sage: CombinatorialFreeModule(QQ, ()).an_element()
0
sage: CombinatorialFreeModule(QQ, ZZ).an_element()
3*B[-1] + B[0] + 3*B[1]
sage: CombinatorialFreeModule(QQ, RR).an_element()
B[1.00000000000000]
"""
x = self.zero()
I = self.basis().keys()
R = self.base_ring()
try:
x = x + self.monomial(I.an_element())
except:
pass
try:
g = iter(self.basis().keys())
for c in range(1,4):
x = x + self.term(g.next(), R(c))
except:
pass
return x
def __contains__(self, x):
"""
TESTS::
sage: F = CombinatorialFreeModule(QQ,["a", "b"])
sage: G = CombinatorialFreeModule(ZZ,["a", "b"])
sage: F.monomial("a") in F
True
sage: G.monomial("a") in F
False
sage: "a" in F
False
sage: 5/3 in F
False
"""
return sage.structure.element.parent(x) == self
def _element_constructor_(self, x):
"""
Coerce x into self.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ,["a", "b"])
sage: F(F.monomial("a")) # indirect doctest
B['a']
Do not rely on the following feature which may be removed in the future::
sage: QS3 = SymmetricGroupAlgebra(QQ,3)
sage: QS3([2,3,1]) # indirect doctest
[2, 3, 1]
instead, use::
sage: P = QS3.basis().keys()
sage: QS3.monomial(P([2,3,1])) # indirect doctest
[2, 3, 1]
or:
sage: B = QS3.basis()
sage: B[P([2,3,1])]
[2, 3, 1]
TODO: The symmetric group algebra (and in general,
combinatorial free modules on word-like object could instead
provide an appropriate short-hand syntax QS3[2,3,1]).
Rationale: this conversion is ambiguous in situations like::
sage: F = CombinatorialFreeModule(QQ,[0,1])
Is ``0`` the zero of the base ring, or the index of a basis
element? I.e. should the result be ``0`` or ``B[0]``?
sage: F = CombinatorialFreeModule(QQ,[0,1])
sage: F(0) # this feature may eventually disappear
0
sage: F(1)
Traceback (most recent call last):
...
TypeError: do not know how to make x (= 1) an element of Free module generated by ... over Rational Field
It is preferable not to rely either on the above, and instead, use::
sage: F.zero()
0
Note that, on the other hand, conversions from the ground ring
are systematically defined (and mathematically meaningful) for
algebras.
Conversions between distinct free modules are not allowed any
more::
sage: F = CombinatorialFreeModule(ZZ, ["a", "b"]); F.rename("F")
sage: G = CombinatorialFreeModule(QQ, ["a", "b"]); G.rename("G")
sage: H = CombinatorialFreeModule(ZZ, ["a", "b", "c"]); H.rename("H")
sage: G(F.monomial("a"))
Traceback (most recent call last):
...
TypeError: do not know how to make x (= B['a']) an element of self (=G)
sage: H(F.monomial("a"))
Traceback (most recent call last):
...
TypeError: do not know how to make x (= B['a']) an element of self (=H)
Here is a real life example illustrating that this yielded
mathematically wrong results::
sage: S = SymmetricFunctions(QQ)
sage: s = S.s(); p = S.p()
sage: ss = tensor([s,s]); pp = tensor([p,p])
sage: a = tensor((s[5],s[5]))
sage: pp(a) # used to yield p[[5]] # p[[5]]
Traceback (most recent call last):
...
NotImplementedError
Extensions of the ground ring should probably be reintroduced
at some point, but via coercions, and with stronger sanity
checks (ensuring that the codomain is really obtained by
extending the scalar of the domain; checking that they share
the same class is not sufficient).
TESTS:
Conversion from the ground ring is implemented for algebras::
sage: QS3 = SymmetricGroupAlgebra(QQ,3)
sage: QS3(2)
2*[1, 2, 3]
"""
R = self.base_ring()
eclass = self.element_class
if isinstance(x, int):
x = Integer(x)
if x in R:
if x == 0:
return self.zero()
else:
raise TypeError, "do not know how to make x (= %s) an element of %s"%(x, self)
elif ((hasattr(self._basis_keys, 'element_class') and
isinstance(self._basis_keys.element_class, type) and
isinstance(x, self._basis_keys.element_class))
or (sage.structure.element.parent(x) == self._basis_keys)):
return self.monomial(x)
elif x in self._basis_keys:
return self.monomial(self._basis_keys(x))
else:
if hasattr(self, '_coerce_end'):
try:
return self._coerce_end(x)
except TypeError:
pass
raise TypeError, "do not know how to make x (= %s) an element of self (=%s)"%(x,self)
def _an_element_impl(self):
"""
Returns an element of self, namely the zero element.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F._an_element_impl()
0
sage: _.parent() is F
True
"""
return self.element_class(self, {})
def combinatorial_class(self):
"""
Returns the combinatorial class that indexes the basis elements.
Deprecated: use self.basis().keys() instead.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.combinatorial_class()
doctest:...: DeprecationWarning: "FM.combinatorial_class()" is deprecated. Use "F.basis().keys()" instead !
{'a', 'b', 'c'}
::
sage: s = SFASchur(QQ)
sage: s.combinatorial_class()
Partitions
"""
from sage.misc.misc import deprecation
deprecation('"FM.combinatorial_class()" is deprecated. Use "F.basis().keys()" instead !')
return self._basis_keys
def dimension(self):
"""
Returns the dimension of the combinatorial algebra (which is given
by the number of elements in the basis).
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.dimension()
3
sage: F.basis().cardinality()
3
sage: F.basis().keys().cardinality()
3
::
sage: s = SFASchur(QQ)
sage: s.dimension()
+Infinity
"""
return self._basis_keys.cardinality()
def set_order(self, order):
"""
Sets the order of the elements of the basis.
If :meth:`set_order` has not been called, then the ordering is
the one used in the generation of the elements of self's
associated enumerated set.
EXAMPLES::
sage: QS2 = SymmetricGroupAlgebra(QQ,2)
sage: b = list(QS2.basis().keys())
sage: b.reverse()
sage: QS2.set_order(b)
sage: QS2.get_order()
[[2, 1], [1, 2]]
"""
self._order = order
def get_order(self):
"""
Returns the order of the elements in the basis.
EXAMPLES::
sage: QS2 = SymmetricGroupAlgebra(QQ,2)
sage: QS2.get_order() # note: order changed on 2009-03-13
[[2, 1], [1, 2]]
"""
if self._order is None:
self._order = list(self.basis().keys())
return self._order
def from_vector(self, vector):
"""
Build an element of self from a (sparse) vector
See self.get_order and the method to_vector of the elements of self
EXAMPLES::
sage: QS3 = SymmetricGroupAlgebra(QQ, 3)
sage: b = QS3.from_vector(vector((2, 0, 0, 0, 0, 4))); b
2*[1, 2, 3] + 4*[3, 2, 1]
sage: a = 2*QS3([1,2,3])+4*QS3([3,2,1])
sage: a == b
True
"""
cc = self.get_order()
return self._from_dict(dict( (cc[index], coeff) for (index,coeff) in vector.iteritems()))
def prefix(self):
"""
Returns the prefix used when displaying elements of self.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.prefix()
'B'
::
sage: X = SchubertPolynomialRing(QQ)
sage: X.prefix()
'X'
"""
return self._print_options['prefix']
def print_options(self, **kwds):
"""
Return the current print options, or set an option.
INPUT: all of the input is optional; if present, it should be
in the form of keyword pairs, such as
``latex_bracket='('``. The allowable keywords are:
- ``prefix``
- ``latex_prefix``
- ``bracket``
- ``latex_bracket``
- ``scalar_mult``
- ``latex_scalar_mult``
- ``tensor_symbol``
- ``monomial_cmp``
See the documentation for :class:`CombinatorialFreeModule` for
descriptions of the effects of setting each of these options.
OUTPUT: if the user provides any input, set the appropriate
option(s) and return nothing. Otherwise, return the
dictionary of settings for print and LaTeX representations.
EXAMPLES::
sage: F = CombinatorialFreeModule(ZZ, [1,2,3], prefix='x')
sage: F.print_options()
{...'prefix': 'x'...}
sage: F.print_options(bracket='(')
sage: F.print_options()
{...'bracket': '('...}
TESTS::
sage: sorted(F.print_options().items())
[('bracket', '('), ('latex_bracket', False), ('latex_prefix', None), ('latex_scalar_mult', None), ('monomial_cmp', <built-in function cmp>), ('prefix', 'x'), ('scalar_mult', '*'), ('tensor_symbol', None)]
"""
if kwds:
for option in kwds:
if option in ['prefix', 'latex_prefix', 'bracket', 'latex_bracket',
'scalar_mult', 'latex_scalar_mult', 'tensor_symbol',
'monomial_cmp'
]:
self._print_options[option] = kwds[option]
else:
raise ValueError, '%s is not a valid print option.' % option
else:
return self._print_options
_repr_option_bracket = True
def _repr_term(self, m):
"""
Returns a string representing the basis element indexed by m.
The output can be customized by setting any of the following
options when initializing the module:
- prefix
- bracket
- scalar_mult
Alternatively, one can use the :meth:`print_options` method
to achieve the same effect. To modify the bracket setting,
one can also set ``self._repr_option_bracket`` as long as one
has *not* set the ``bracket`` option: if the
``bracket`` option is anything but ``None``, it overrides
the value of ``self._repr_option_bracket``.
See the documentation for :class:`CombinatorialFreeModule` for
details on the initialization options.
.. todo:: rename to ``_repr_monomial``
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: e = F.basis()
sage: e['a'] + 2*e['b'] # indirect doctest
B['a'] + 2*B['b']
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'], prefix="F")
sage: e = F.basis()
sage: e['a'] + 2*e['b'] # indirect doctest
F['a'] + 2*F['b']
sage: QS3 = CombinatorialFreeModule(QQ, Permutations(3), prefix="")
sage: a = 2*QS3([1,2,3])+4*QS3([3,2,1])
sage: a # indirect doctest
2*[[1, 2, 3]] + 4*[[3, 2, 1]]
sage: QS3.print_options(bracket = False)
sage: a # indirect doctest
2*[1, 2, 3] + 4*[3, 2, 1]
sage: QS3.print_options(prefix='')
sage: a # indirect doctest
2*[1, 2, 3] + 4*[3, 2, 1]
sage: QS3.print_options(bracket="|", scalar_mult=" *@* ")
sage: a # indirect doctest
2 *@* |[1, 2, 3]| + 4 *@* |[3, 2, 1]|
TESTS::
sage: F = CombinatorialFreeModule(QQ, [('a', 'b'), ('c','d')])
sage: e = F.basis()
sage: e[('a','b')] + 2*e[('c','d')] # indirect doctest
B[('a', 'b')] + 2*B[('c', 'd')]
"""
bracket = self._print_options.get('bracket', None)
bracket_d = {"{": "}", "[": "]", "(": ")"}
if bracket is None:
bracket = self._repr_option_bracket
if bracket is True:
left = "["
right = "]"
elif bracket is False:
left = ""
right = ""
elif isinstance(bracket, (tuple, list)):
left = bracket[0]
right = bracket[1]
elif bracket in bracket_d:
left = bracket
right = bracket_d[bracket]
else:
left = bracket
right = bracket
return self.prefix() + left + repr(m) + right
def _latex_term(self, m):
"""
Returns a string for the LaTeX code for the basis element
indexed by m.
The output can be customized by setting any of the following
options when initializing the module:
- prefix
- latex_prefix
- latex_bracket
(Alternatively, one can use the :meth:`print_options` method
to achieve the same effect.)
See the documentation for :class:`CombinatorialFreeModule` for
details on the initialization options.
.. todo:: rename to ``_latex_monomial``
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: e = F.basis()
sage: latex(e['a'] + 2*e['b']) # indirect doctest
B_{a} + 2B_{b}
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'], prefix="C")
sage: e = F.basis()
sage: latex(e['a'] + 2*e['b']) # indirect doctest
C_{a} + 2C_{b}
sage: QS3 = CombinatorialFreeModule(QQ, Permutations(3), prefix="", scalar_mult="*")
sage: a = 2*QS3([1,2,3])+4*QS3([3,2,1])
sage: latex(a) # indirect doctest
2[1, 2, 3] + 4[3, 2, 1]
sage: QS3.print_options(latex_bracket=True)
sage: latex(a) # indirect doctest
2\left[[1, 2, 3]\right] + 4\left[[3, 2, 1]\right]
sage: QS3.print_options(latex_bracket="(")
sage: latex(a) # indirect doctest
2\left([1, 2, 3]\right) + 4\left([3, 2, 1]\right)
sage: QS3.print_options(latex_bracket=('\\myleftbracket', '\\myrightbracket'))
sage: latex(a) # indirect doctest
2\myleftbracket[1, 2, 3]\myrightbracket + 4\myleftbracket[3, 2, 1]\myrightbracket
TESTS::
sage: F = CombinatorialFreeModule(QQ, [('a', 'b'), (0,1,2)])
sage: e = F.basis()
sage: latex(e[('a','b')]) # indirect doctest
B_{\left(a, b\right)}
sage: latex(2*e[(0,1,2)]) # indirect doctest
2B_{\left(0, 1, 2\right)}
sage: F = CombinatorialFreeModule(QQ, [('a', 'b'), (0,1,2)], prefix="")
sage: e = F.basis()
sage: latex(2*e[(0,1,2)]) # indirect doctest
2\left(0, 1, 2\right)
"""
from sage.misc.latex import latex
s = latex(m)
if s.find('\\verb') != -1:
import re
s = re.sub("\\\\verb(.)(.*?)\\1", "\\2", s)
s = s.replace("\\phantom{x}", " ")
bracket_d = {"{": "\\}", "[": "]", "(": ")", "\\{": "\\}",
"|": "|", "||": "||"}
bracket = self._print_options.get('latex_bracket', False)
if bracket is True:
left = "\\left["
right = "\\right]"
elif bracket is False:
left = ""
right = ""
elif isinstance(bracket, (tuple, list)):
left = bracket[0]
right = bracket[1]
elif bracket in bracket_d:
left = bracket
right = bracket_d[bracket]
if left == "{":
left = "\\{"
left = "\\left" + left
right = "\\right" + right
else:
left = bracket
right = bracket
prefix = self._print_options.get('latex_prefix')
if prefix is None:
prefix = self._print_options.get('prefix')
if prefix == "":
return left + s + right
return "%s_{%s}" % (prefix, s)
def __cmp__(self, other):
"""
EXAMPLES::
sage: XQ = SchubertPolynomialRing(QQ)
sage: XZ = SchubertPolynomialRing(ZZ)
sage: XQ == XZ #indirect doctest
False
sage: XQ == XQ
True
"""
if not isinstance(other, self.__class__):
return -1
c = cmp(self.base_ring(), other.base_ring())
if c: return c
return 0
def _apply_module_morphism( self, x, on_basis, codomain=False ):
"""
Returns the image of x under the module morphism defined by
extending f by linearity.
INPUT:
- ``x`` : a element of self
- ``on_basis`` - a function that takes in a combinatorial
object indexing a basis element and returns an element of the
codomain
- ``codomain`` (optional) - the codomain of the morphism, otherwise it is computed using on_basis
EXAMPLES::
sage: s = SFASchur(QQ)
sage: a = s([3]) + s([2,1]) + s([1,1,1])
sage: b = 2*a
sage: f = lambda part: Integer( len(part) )
sage: s._apply_module_morphism(a, f) #1+2+3
6
sage: s._apply_module_morphism(b, f) #2*(1+2+3)
12
"""
if x == self.zero():
if not codomain:
B = self.basis()
keys = list( B.keys() )
if len( keys ) > 0:
key = keys[0]
codomain = on_basis( key ).parent()
else:
raise ValueError, 'Codomain could not be determined'
return codomain.zero()
else:
if not codomain:
keys = x.support()
key = keys[0]
codomain = on_basis( key ).parent()
if hasattr( codomain, 'linear_combination' ):
return codomain.linear_combination( ( on_basis( key ), coeff ) for key, coeff in x._monomial_coefficients.iteritems() )
else:
return_sum = codomain.zero()
for key, coeff in x._monomial_coefficients.iteritems():
return_sum += coeff * on_basis( key )
return return_sum
def _apply_module_endomorphism(self, x, on_basis):
"""
This takes in a function from the basis elements to the elements of
self and applies it linearly to a. Note that
_apply_module_endomorphism does not require multiplication on
self to be defined.
EXAMPLES::
sage: s = SFASchur(QQ)
sage: f = lambda part: 2*s(part.conjugate())
sage: s._apply_module_endomorphism( s([2,1]) + s([1,1,1]), f)
2*s[2, 1] + 2*s[3]
"""
return self.linear_combination( ( on_basis( key ), coeff ) for key, coeff in x._monomial_coefficients.iteritems() )
def sum(self, iter_of_elements):
"""
overrides method inherited from commutative additive monoid as it is much faster on dicts directly
INPUT:
- ``iter_of_elements``: iterator of elements of ``self``
Returns the sum of all elements in ``iter_of_elements``
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ,[1,2])
sage: f = F.an_element(); f
2*B[1] + 2*B[2]
sage: F.sum( f for _ in range(5) )
10*B[1] + 10*B[2]
"""
D = dict_addition( element._monomial_coefficients for element in iter_of_elements )
return self._from_dict( D, remove_zeros=False )
def linear_combination( self, iter_of_elements_coeff, factor_on_left=True ):
"""
INPUT:
- ``iter_of_elements_coeff`` -- iterator of pairs ``(element, coeff)``
with ``element`` in ``self`` and ``coeff`` in ``self.base_ring()``
- ``factor_on_left`` (optional) -- if ``True``, the coefficients are
multiplied from the left if ``False``, the coefficients are
multiplied from the right
Returns the linear combination `\lambda_1 v_1 + ... + \lambda_k v_k`
(resp. the linear combination `v_1 \lambda_1 + ... + v_k \lambda_k`)
where ``iter_of_elements_coeff`` iterates through the sequence
`(\lambda_1, v_1) ... (\lambda_k, v_k)`.
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ,[1,2])
sage: f = F.an_element(); f
2*B[1] + 2*B[2]
sage: F.linear_combination( (f,i) for i in range(5) )
20*B[1] + 20*B[2]
"""
return self._from_dict( dict_linear_combination( ( ( element._monomial_coefficients, coeff ) for element, coeff in iter_of_elements_coeff ), factor_on_left=factor_on_left ), remove_zeros=False )
def term(self, index, coeff=None):
"""
Constructs a term in ``self``
INPUT:
- ``index`` -- the index of a basis element
- ``coeff`` -- an element of the coefficient ring (default: one)
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.term('a',3)
3*B['a']
sage: F.term('a')
B['a']
Design: should this do coercion on the coefficient ring?
"""
if coeff is None:
coeff = self.base_ring().one()
return self._from_dict( {index: coeff} )
def _monomial(self, index):
"""
TESTS::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F._monomial('a')
B['a']
"""
return self._from_dict( {index: self.base_ring().one()}, remove_zeros = False )
@lazy_attribute
def monomial(self):
"""
INPUT:
- ''i''
Returns the basis element indexed by i
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.monomial('a')
B['a']
F.monomial is in fact (almost) a map::
sage: F.monomial
Term map from {'a', 'b', 'c'} to Free module generated by {'a', 'b', 'c'} over Rational Field
"""
return PoorManMap(self._monomial, domain = self._basis_keys, codomain = self, name = "Term map")
def _sum_of_monomials(self, indices):
"""
TESTS::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F._sum_of_monomials(['a', 'b'])
B['a'] + B['b']
"""
return self.sum(self.monomial(index) for index in indices)
@lazy_attribute
def sum_of_monomials(self):
"""
INPUT:
- ''indices'' -- an list (or iterable) of indices of basis elements
Returns the sum of the corresponding basis elements
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.sum_of_monomials(['a', 'b'])
B['a'] + B['b']
sage: F.sum_of_monomials(['a', 'b', 'a'])
2*B['a'] + B['b']
F.sum_of_monomials is in fact (almost) a map::
sage: F.sum_of_monomials
A map to Free module generated by {'a', 'b', 'c'} over Rational Field
"""
return PoorManMap(self._sum_of_monomials, codomain = self)
def sum_of_terms(self, terms, distinct=False):
"""
Constructs a sum of terms of ``self``
INPUT:
- ``terms`` -- a list (or iterable) of pairs (index, coeff)
- ``distinct`` -- whether the indices are guaranteed to be distinct (default: ``False``)
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.sum_of_terms([('a',2), ('c',3)])
2*B['a'] + 3*B['c']
If ``distinct`` is True, then the construction is optimized::
sage: F.sum_of_terms([('a',2), ('c',3)], distinct = True)
2*B['a'] + 3*B['c']
.. warning::
Use ``distinct=True`` only if you are sure that the
indices are indeed distinct::
sage: F.sum_of_terms([('a',2), ('a',3)], distinct = True)
3*B['a']
Extreme case::
sage: F.sum_of_terms([])
0
"""
if distinct:
return self._from_dict(dict(terms))
return self.sum(self.term(index, coeff) for (index, coeff) in terms)
def monomial_or_zero_if_none(self, i):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.monomial_or_zero_if_none('a')
B['a']
sage: F.monomial_or_zero_if_none(None)
0
"""
if i == None:
return self.zero()
return self.monomial(i)
@cached_method
def zero(self):
"""
EXAMPLES::
sage: F = CombinatorialFreeModule(QQ, ['a', 'b', 'c'])
sage: F.zero()
0
"""
return self._from_dict({}, remove_zeros=False)
def _from_dict( self, d, coerce=False, remove_zeros=True ):
"""
Construct an element of ``self`` from an `{index: coefficient}` dictionary
INPUT:
- ``d`` -- a dictionary ``{index: coeff}`` where each ``index`` is the
index of a basis element and each ``coeff`` belongs to the
coefficient ring ``self.base_ring()``
- ``coerce`` -- a boolean (default: ``False``), whether to coerce the
``coeff``s to the coefficient ring
- ``remove_zeros`` -- a boolean (default: ``True``), if some
``coeff``s may be zero and should therefore be removed
EXAMPLES::
sage: e = SFAElementary(QQ)
sage: s = SFASchur(QQ)
sage: a = e([2,1]) + e([1,1,1]); a
e[1, 1, 1] + e[2, 1]
sage: s._from_dict(a.monomial_coefficients())
s[1, 1, 1] + s[2, 1]
If the optional argument ``coerce`` is ``True``, then the
coefficients are coerced into the base ring of ``self``::
sage: part = Partition([2,1])
sage: d = {part:1}
sage: a = s._from_dict(d,coerce=True); a
s[2, 1]
sage: a.coefficient(part).parent()
Rational Field
With ``remove_zeros=True``, zero coefficients are removed::
sage: s._from_dict({part:0})
0
.. warning::
With ``remove_zeros=True``, it is assumed that no
coefficient of the dictionary is zero. Otherwise, this may
lead to illegal results::
sage: list(s._from_dict({part:0}, remove_zeros=False))
[([2, 1], 0)]
"""
assert isinstance(d, dict)
if coerce:
R = self.base_ring()
d = dict( (key, R(coeff)) for key,coeff in d.iteritems())
if remove_zeros:
d = dict( (key, coeff) for key, coeff in d.iteritems() if coeff)
return self.element_class( self, d )
class CombinatorialFreeModule_Tensor(CombinatorialFreeModule):
"""
Tensor Product of Free Modules
EXAMPLES:
We construct two free modules, assign them short names, and construct their tensor product::
sage: F = CombinatorialFreeModule(ZZ, [1,2]); F.__custom_name = "F"
sage: G = CombinatorialFreeModule(ZZ, [3,4]); G.__custom_name = "G"
sage: T = tensor([F, G]); T
F # G
sage: T.category()
Category of tensor products of modules with basis over Integer Ring
sage: T.construction() # todo: not implemented
[tensor, ]
T is a free module, with same base ring as F and G::
sage: T.base_ring()
Integer Ring
The basis of T is indexed by tuples of basis indices of F and G::
sage: T.basis().keys()
Image of Cartesian product of {1, 2}, {3, 4} by <type 'tuple'>
sage: T.basis().keys().list()
[(1, 3), (1, 4), (2, 3), (2, 4)]
FIXME: Should elements of a CartesianProduct be tuples (making them hashable)?
Here are the basis elements themselves::
sage: T.basis().cardinality()
4
sage: list(T.basis())
[B[1] # B[3], B[1] # B[4], B[2] # B[3], B[2] # B[4]]
The tensor product is associative and flattens sub tensor products::
sage: H = CombinatorialFreeModule(ZZ, [5,6]); H.rename("H")
sage: tensor([F, tensor([G, H])])
F # G # H
sage: tensor([tensor([F, G]), H])
F # G # H
sage: tensor([F, G, H])
F # G # H
We now compute the tensor product of elements of free modules::
sage: f = F.monomial(1) + 2 * F.monomial(2)
sage: g = 2*G.monomial(3) + G.monomial(4)
sage: h = H.monomial(5) + H.monomial(6)
sage: tensor([f, g])
2*B[1] # B[3] + B[1] # B[4] + 4*B[2] # B[3] + 2*B[2] # B[4]
Again, the tensor product is associative on elements::
sage: tensor([f, tensor([g, h])]) == tensor([f, g, h])
True
sage: tensor([tensor([f, g]), h]) == tensor([f, g, h])
True
Note further that the tensor product spaces need not preexist::
sage: t = tensor([f, g, h])
sage: t.parent()
F # G # H
TESTS::
sage: tensor([tensor([F, G]), H]) == tensor([F, G, H])
True
sage: tensor([F, tensor([G, H])]) == tensor([F, G, H])
True
"""
@staticmethod
def __classcall_private__(cls, modules, **options):
"""
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [1,2])
sage: G = CombinatorialFreeModule(ZZ, [3,4])
sage: H = CombinatorialFreeModule(ZZ, [4])
sage: tensor([tensor([F, G]), H]) == tensor([F, G, H])
True
sage: tensor([F, tensor([G, H])]) == tensor([F, G, H])
True
"""
assert(len(modules) > 0)
R = modules[0].base_ring()
assert(all(module in ModulesWithBasis(R)) for module in modules)
modules = sum([module._sets if isinstance(module, CombinatorialFreeModule_Tensor) else (module,) for module in modules], ())
return super(CombinatorialFreeModule.Tensor, cls).__classcall__(cls, modules, **options)
def __init__(self, modules, **options):
"""
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [1,2]); F
F
"""
from sage.categories.tensor import tensor
self._sets = modules
CombinatorialFreeModule.__init__(self, modules[0].base_ring(), CartesianProduct(*[module.basis().keys() for module in modules]).map(tuple), **options)
self._print_options['tensor_symbol'] = options.get('tensor_symbol', tensor.symbol)
def _repr_(self):
"""
This is customizable by setting
``self.print_options('tensor_symbol'=...)``.
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [1,2,3])
sage: G = CombinatorialFreeModule(ZZ, [1,2,3,8])
sage: F.rename("F")
sage: G.rename("G")
sage: T = tensor([F, G])
sage: T # indirect doctest
F # G
sage: T.print_options(tensor_symbol= ' @ ') # note the spaces
sage: T # indirect doctest
F @ G
"""
from sage.categories.tensor import tensor
if hasattr(self, "_print_options"):
symb = self._print_options['tensor_symbol']
if symb is None:
symb = tensor.symbol
else:
symb = tensor.symbol
return symb.join(["%s"%module for module in self._sets])
def _latex_(self):
"""
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [1,2,3])
sage: G = CombinatorialFreeModule(ZZ, [1,2,3,8])
sage: F.rename("F")
sage: G.rename("G")
sage: latex(tensor([F, F, G])) # indirect doctest
\verb|F| \otimes \verb|F| \otimes \verb|G|
sage: F._latex_ = lambda : "F"
sage: G._latex_ = lambda : "G"
sage: latex(tensor([F, F, G])) # indirect doctest
F \otimes F \otimes G
"""
from sage.misc.latex import latex
symb = " \\otimes "
return symb.join(["%s"%latex(module) for module in self._sets])
def _repr_term(self, term):
"""
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [1,2,3], prefix="F")
sage: G = CombinatorialFreeModule(ZZ, [1,2,3,4], prefix="G")
sage: f = F.monomial(1) + 2 * F.monomial(2)
sage: g = 2*G.monomial(3) + G.monomial(4)
sage: tensor([f, g]) # indirect doctest
2*F[1] # G[3] + F[1] # G[4] + 4*F[2] # G[3] + 2*F[2] # G[4]
"""
from sage.categories.tensor import tensor
if hasattr(self, "_print_options"):
symb = self._print_options['tensor_symbol']
if symb is None:
symb = tensor.symbol
else:
symb = tensor.symbol
return symb.join(module._repr_term(t) for (module, t) in zip(self._sets, term))
def _latex_term(self, term):
"""
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [1,2,3], prefix='x')
sage: G = CombinatorialFreeModule(ZZ, [1,2,3,4], prefix='y')
sage: f = F.monomial(1) + 2 * F.monomial(2)
sage: g = 2*G.monomial(3) + G.monomial(4)
sage: latex(tensor([f, g])) # indirect doctest
2x_{1} \otimes y_{3} + x_{1} \otimes y_{4} + 4x_{2} \otimes y_{3} + 2x_{2} \otimes y_{4}
"""
symb = " \\otimes "
return symb.join(module._latex_term(t) for (module, t) in zip(self._sets, term))
@cached_method
def tensor_constructor(self, modules):
r"""
INPUT:
- ``modules`` -- a tuple `(F_1,\dots,F_n)` of
free modules whose tensor product is self
Returns the canonical multilinear morphism from
`F_1 \times \dots \times F_n` to `F_1 \otimes \dots \otimes F_n`
EXAMPLES::
sage: F = CombinatorialFreeModule(ZZ, [1,2]); F.__custom_name = "F"
sage: G = CombinatorialFreeModule(ZZ, [3,4]); G.__custom_name = "G"
sage: H = CombinatorialFreeModule(ZZ, [5,6]); H.rename("H")
sage: f = F.monomial(1) + 2 * F.monomial(2)
sage: g = 2*G.monomial(3) + G.monomial(4)
sage: h = H.monomial(5) + H.monomial(6)
sage: FG = tensor([F, G ])
sage: phi_fg = FG.tensor_constructor((F, G))
sage: phi_fg(f,g)
2*B[1] # B[3] + B[1] # B[4] + 4*B[2] # B[3] + 2*B[2] # B[4]
sage: FGH = tensor([F, G, H])
sage: phi_fgh = FGH.tensor_constructor((F, G, H))
sage: phi_fgh(f, g, h)
2*B[1] # B[3] # B[5] + 2*B[1] # B[3] # B[6] + B[1] # B[4] # B[5] + B[1] # B[4] # B[6] + 4*B[2] # B[3] # B[5] + 4*B[2] # B[3] # B[6] + 2*B[2] # B[4] # B[5] + 2*B[2] # B[4] # B[6]
sage: phi_fg_h = FGH.tensor_constructor((FG, H))
sage: phi_fg_h(phi_fg(f, g), h)
2*B[1] # B[3] # B[5] + 2*B[1] # B[3] # B[6] + B[1] # B[4] # B[5] + B[1] # B[4] # B[6] + 4*B[2] # B[3] # B[5] + 4*B[2] # B[3] # B[6] + 2*B[2] # B[4] # B[5] + 2*B[2] # B[4] # B[6]
"""
assert(module in ModulesWithBasis(self.base_ring()) for module in modules)
assert(sage.categories.tensor.tensor(modules) == self)
is_tensor = [isinstance(module, CombinatorialFreeModule_Tensor) for module in modules]
result = self.monomial * CartesianProductWithFlattening(is_tensor)
for i in range(0, len(modules)):
result = modules[i]._module_morphism(result, position = i, codomain = self)
return result
def _tensor_of_elements(self, elements):
"""
Returns the tensor product of the specified elements.
The result should be in self.
EXAMPLES::
sage: F = CombinatorialFreeModule(ZZ, [1,2]); F.__custom_name = "F"
sage: G = CombinatorialFreeModule(ZZ, [3,4]); G.__custom_name = "G"
sage: H = CombinatorialFreeModule(ZZ, [5,6]); H.rename("H")
sage: f = F.monomial(1) + 2 * F.monomial(2)
sage: g = 2*G.monomial(3) + G.monomial(4)
sage: h = H.monomial(5) + H.monomial(6)
sage: GH = tensor([G, H])
sage: gh = GH._tensor_of_elements([g, h]); gh
2*B[3] # B[5] + 2*B[3] # B[6] + B[4] # B[5] + B[4] # B[6]
sage: FGH = tensor([F, G, H])
sage: FGH._tensor_of_elements([f, g, h])
2*B[1] # B[3] # B[5] + 2*B[1] # B[3] # B[6] + B[1] # B[4] # B[5] + B[1] # B[4] # B[6] + 4*B[2] # B[3] # B[5] + 4*B[2] # B[3] # B[6] + 2*B[2] # B[4] # B[5] + 2*B[2] # B[4] # B[6]
sage: FGH._tensor_of_elements([f, gh])
2*B[1] # B[3] # B[5] + 2*B[1] # B[3] # B[6] + B[1] # B[4] # B[5] + B[1] # B[4] # B[6] + 4*B[2] # B[3] # B[5] + 4*B[2] # B[3] # B[6] + 2*B[2] # B[4] # B[5] + 2*B[2] # B[4] # B[6]
"""
return self.tensor_constructor(tuple(element.parent() for element in elements))(*elements)
class CartesianProductWithFlattening(object):
"""
A class for cartesian product constructor, with partial flattening
"""
def __init__(self, flatten):
"""
INPUT:
- ``flatten`` -- a tuple of booleans
This constructs a callable which accepts ``len(flatten)``
arguments, and builds a tuple out them. When ``flatten[i]``,
the i-th argument itself should be a tuple which is flattened
in the result.
sage: from sage.combinat.free_module import CartesianProductWithFlattening
sage: CartesianProductWithFlattening([True, False, True, True])
<sage.combinat.free_module.CartesianProductWithFlattening object at ...>
"""
self._flatten = flatten
def __call__(self, *indices):
"""
EXAMPLES::
sage: from sage.combinat.free_module import CartesianProductWithFlattening
sage: cp = CartesianProductWithFlattening([True, False, True, True])
sage: cp((1,2), (3,4), (5,6), (7,8))
(1, 2, (3, 4), 5, 6, 7, 8)
sage: cp((1,2,3), 4, (5,6), (7,8))
(1, 2, 3, 4, 5, 6, 7, 8)
"""
return sum( (i if flatten else (i,) for (i,flatten) in zip(indices, self._flatten) ), ())
CombinatorialFreeModule.Tensor = CombinatorialFreeModule_Tensor
class CombinatorialFreeModule_CartesianProduct(CombinatorialFreeModule):
"""
An implementation of cartesian products of modules with basis
EXAMPLES:
We construct two free modules, assign them short names, and construct their cartesian product::
sage: F = CombinatorialFreeModule(ZZ, [4,5]); F.__custom_name = "F"
sage: G = CombinatorialFreeModule(ZZ, [4,6]); G.__custom_name = "G"
sage: H = CombinatorialFreeModule(ZZ, [4,7]); H.__custom_name = "H"
sage: S = cartesian_product([F, G])
sage: S
F (+) G
sage: S.basis()
Lazy family (Term map from Disjoint union of Family ({4, 5}, {4, 6}) to F (+) G(i))_{i in Disjoint union of Family ({4, 5}, {4, 6})}
Note that the indices of the basis elements of F and G intersect non
trivially. This is handled by forcing the union to be disjoint::
sage: list(S.basis())
[B[(0, 4)], B[(0, 5)], B[(1, 4)], B[(1, 6)]]
We now compute the cartesian product of elements of free modules::
sage: f = F.monomial(4) + 2 * F.monomial(5)
sage: g = 2*G.monomial(4) + G.monomial(6)
sage: h = H.monomial(4) + H.monomial(7)
sage: cartesian_product([f,g])
B[(0, 4)] + 2*B[(0, 5)] + 2*B[(1, 4)] + B[(1, 6)]
sage: cartesian_product([f,g,h])
B[(0, 4)] + 2*B[(0, 5)] + 2*B[(1, 4)] + B[(1, 6)] + B[(2, 4)] + B[(2, 7)]
sage: cartesian_product([f,g,h]).parent()
F (+) G (+) H
TODO: choose an appropriate semantic for cartesian products of cartesian products (associativity?)::
sage: S = cartesian_product([cartesian_product([F, G]), H]) # todo: not implemented
F (+) G (+) H
"""
def __init__(self, modules, **options):
r"""
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [2,4,5])
sage: G = CombinatorialFreeModule(ZZ, [2,4,7])
sage: cartesian_product([F, G])
Free module generated by {2, 4, 5} over Integer Ring (+) Free module generated by {2, 4, 7} over Integer Ring
"""
assert(len(modules) > 0)
R = modules[0].base_ring()
assert(all(module in ModulesWithBasis(R)) for module in modules)
self._sets = modules
CombinatorialFreeModule.__init__(self, R,
DisjointUnionEnumeratedSets(
[module.basis().keys() for module in modules], keepkey=True),
**options)
def _sets_keys(self):
"""
In waiting for self._sets.keys()
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [2,4,5])
sage: G = CombinatorialFreeModule(ZZ, [2,4,7])
sage: CP = cartesian_product([F, G])
sage: CP._sets_keys()
[0, 1]
"""
return range(len(self._sets))
def _repr_(self):
"""
TESTS::
sage: F = CombinatorialFreeModule(ZZ, [2,4,5])
sage: CP = cartesian_product([F, F]); CP # indirect doctest
Free module generated by {2, 4, 5} over Integer Ring (+) Free module generated by {2, 4, 5} over Integer Ring
sage: F.__custom_name = "F"; CP
F (+) F
"""
from sage.categories.cartesian_product import cartesian_product
return cartesian_product.symbol.join(["%s"%module for module in self._sets])
@cached_method
def summand_embedding(self, i):
"""
Returns the natural embedding morphism of the i-th summand of self into self
INPUTS:
- ``i`` -- an integer
EXAMPLES::
sage: F = CombinatorialFreeModule(ZZ, [4,5]); F.__custom_name = "F"
sage: G = CombinatorialFreeModule(ZZ, [4,6]); G.__custom_name = "G"
sage: S = cartesian_product([F, G])
sage: phi = S.summand_embedding(0)
sage: phi(F.monomial(4) + 2 * F.monomial(5))
B[(0, 4)] + 2*B[(0, 5)]
sage: phi(F.monomial(4) + 2 * F.monomial(6)).parent() == S
True
sage: phi(G.monomial(4)) # not implemented Should raise an error! problem: G(F.monomial(4)) does not complain!!!!
"""
assert i in self._sets_keys()
return self._sets[i]._module_morphism(lambda t: self.monomial((i,t)), codomain = self)
@cached_method
def summand_projection(self, i):
"""
Returns the natural projection onto the i-th summand of self
INPUTS:
- ``i`` -- an integer
EXAMPLE::
sage: F = CombinatorialFreeModule(ZZ, [4,5]); F.__custom_name = "F"
sage: G = CombinatorialFreeModule(ZZ, [4,6]); G.__custom_name = "G"
sage: S = cartesian_product([F, G])
sage: x = S.monomial((0,4)) + 2 * S.monomial((0,5)) + 3 * S.monomial((1,6))
sage: S.summand_projection(0)(x)
B[4] + 2*B[5]
sage: S.summand_projection(1)(x)
3*B[6]
sage: S.summand_projection(0)(x).parent() == F
True
sage: S.summand_projection(1)(x).parent() == G
True
"""
assert i in self._sets_keys()
module = self._sets[i]
return self._module_morphism(lambda (j,t): module.monomial(t) if i == j else module.zero(), codomain = module)
def _cartesian_product_of_elements(self, elements):
"""
Returns the cartesian product of the elements
INPUT:
- ``elements`` - a tuple with one element of each summand of self
EXAMPLES::
sage: F = CombinatorialFreeModule(ZZ, [4,5]); F.__custom_name = "F"
sage: G = CombinatorialFreeModule(ZZ, [4,6]); G.__custom_name = "G"
sage: S = cartesian_product([F, G])
sage: f = F.monomial(4) + 2 * F.monomial(5)
sage: g = 2*G.monomial(4) + G.monomial(6)
sage: S._cartesian_product_of_elements([f, g])
B[(0, 4)] + 2*B[(0, 5)] + 2*B[(1, 4)] + B[(1, 6)]
sage: S._cartesian_product_of_elements([f, g]).parent() == S
True
"""
return self.sum(self.summand_embedding(i)(elements[i]) for i in self._sets_keys())
class Element(CombinatorialFreeModule.Element):
pass
CombinatorialFreeModule.CartesianProduct = CombinatorialFreeModule_CartesianProduct
