X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=mjo%2Fmatrix_algebra.py;h=29a37d1e7c9bdee3dee6b36960126d5f545753fe;hb=9c7fc4d836d337fcba8846ee4538bb0571c60f08;hp=d67347b3aa1252acaf165448d1ea35ebb4a77cd7;hpb=d0c6baf5cd567617f96a2a598123052409b33c94;p=sage.d.git diff --git a/mjo/matrix_algebra.py b/mjo/matrix_algebra.py index d67347b..29a37d1 100644 --- a/mjo/matrix_algebra.py +++ b/mjo/matrix_algebra.py @@ -57,8 +57,18 @@ class MatrixAlgebraElement(IndexedFreeModuleElement): | 0 | 0 | +---+---+ + TESTS:: + + sage: MatrixAlgebra(0,ZZ,ZZ).zero() + 0 + """ - return table(self.rows(), frame=True)._repr_() + if self.nrows() == 0 or self.ncols() == 0: + # Otherwise we get a crash or a blank space, depending + # on how hard we work for it. + return self.parent().entry_algebra().zero().__repr__() + + return table(rs, frame=True)._repr_() def list(self): @@ -185,9 +195,8 @@ class MatrixAlgebra(CombinatorialFreeModule): if "Unital" in entry_algebra.category().axioms(): category = category.Unital() entry_one = entry_algebra.one() - self.one = lambda: sum( (self.monomial((i,i,entry_one)) - for i in range(self.nrows()) ), - self.zero() ) + self.one = lambda: self.sum( (self.monomial((i,i,entry_one)) + for i in range(self.nrows()) ) ) if "Associative" in entry_algebra.category().axioms(): category = category.Associative() @@ -198,8 +207,6 @@ class MatrixAlgebra(CombinatorialFreeModule): # sticking a "1" in each position doesn't give us a basis for # the space. We actually need to stick each of e0, e1, ... (a # basis for the entry algebra itself) into each position. - I = range(n) - J = range(n) self._entry_algebra = entry_algebra # Needs to make the (overridden) method call when, for example, @@ -242,6 +249,81 @@ class MatrixAlgebra(CombinatorialFreeModule): """ return self.entry_algebra().gens() + def _entry_algebra_element_to_vector(self, entry): + r""" + Return a vector representation (of length equal to the cardinality + of :meth:`entry_algebra_gens`) of the given ``entry``. + + This can be overridden in subclasses to work around the fact that + real numbers, complex numbers, quaternions, et cetera, all require + different incantations to turn them into a vector. + + It only makes sense to "guess" here in the superclass when no + subclass that overrides :meth:`entry_algebra_gens` exists. So + if you have a special subclass for your annoying entry algebra, + override this with the correct implementation there instead of + adding a bunch of awkward cases to this superclass method. + + SETUP:: + + sage: from mjo.hurwitz import Octonions + sage: from mjo.matrix_algebra import MatrixAlgebra + + EXAMPLES: + + Real numbers:: + + sage: A = MatrixAlgebra(1, AA, QQ) + sage: A._entry_algebra_element_to_vector(AA(17)) + (17) + + Octonions:: + + sage: A = MatrixAlgebra(1, Octonions(), QQ) + sage: e = A.entry_algebra_gens() + sage: A._entry_algebra_element_to_vector(e[0]) + (1, 0, 0, 0, 0, 0, 0, 0) + sage: A._entry_algebra_element_to_vector(e[1]) + (0, 1, 0, 0, 0, 0, 0, 0) + sage: A._entry_algebra_element_to_vector(e[2]) + (0, 0, 1, 0, 0, 0, 0, 0) + sage: A._entry_algebra_element_to_vector(e[3]) + (0, 0, 0, 1, 0, 0, 0, 0) + sage: A._entry_algebra_element_to_vector(e[4]) + (0, 0, 0, 0, 1, 0, 0, 0) + sage: A._entry_algebra_element_to_vector(e[5]) + (0, 0, 0, 0, 0, 1, 0, 0) + sage: A._entry_algebra_element_to_vector(e[6]) + (0, 0, 0, 0, 0, 0, 1, 0) + sage: A._entry_algebra_element_to_vector(e[7]) + (0, 0, 0, 0, 0, 0, 0, 1) + + Sage matrices:: + + sage: MS = MatrixSpace(QQ,2) + sage: A = MatrixAlgebra(1, MS, QQ) + sage: A._entry_algebra_element_to_vector(MS([[1,2],[3,4]])) + (1, 2, 3, 4) + + """ + if hasattr(entry, 'to_vector'): + return entry.to_vector() + + from sage.modules.free_module import FreeModule + d = len(self.entry_algebra_gens()) + V = FreeModule(self.entry_algebra().base_ring(), d) + + if hasattr(entry, 'list'): + # sage matrices + return V(entry.list()) + + # This works in AA, and will crash if it doesn't know what to + # do, and that's fine because then I don't know what to do + # either. + return V((entry,)) + + + def nrows(self): return self._nrows ncols = nrows @@ -272,13 +354,17 @@ class MatrixAlgebra(CombinatorialFreeModule): (i,j,e1) = mon1 (k,l,e2) = mon2 if j == k: - # If e1*e2 has a negative sign in front of it, - # then (i,l,e1*e2) won't be a monomial! - p = e1*e2 - if (i,l,p) in self.indices(): - return self.monomial((i,l,p)) - else: - return -self.monomial((i,l,-p)) + # There's no reason to expect e1*e2 to itself be a monomial, + # so we have to do some manual conversion to get one. + p = self._entry_algebra_element_to_vector(e1*e2) + + # We have to convert alpha_g because a priori it lives in the + # base ring of the entry algebra. + R = self.base_ring() + return self.sum_of_terms( (((i,l,g), R(alpha_g)) + for (alpha_g, g) + in zip(p, self.entry_algebra_gens()) ), + distinct=True) else: return self.zero() @@ -289,17 +375,20 @@ class MatrixAlgebra(CombinatorialFreeModule): SETUP:: - sage: from mjo.matrix_algebra import MatrixAlgebra + sage: from mjo.hurwitz import ComplexMatrixAlgebra EXAMPLES:: - sage: A = MatrixAlgebra(2, QQbar, ZZ) - sage: A.from_list([[0,I],[-I,0]]) + sage: A = ComplexMatrixAlgebra(2, QQbar, ZZ) + sage: M = A.from_list([[0,I],[-I,0]]) + sage: M +----+---+ | 0 | I | +----+---+ | -I | 0 | +----+---+ + sage: M.to_vector() + (0, 0, 0, 1, 0, -1, 0, 0) """ nrows = len(entries) @@ -327,10 +416,23 @@ class MatrixAlgebra(CombinatorialFreeModule): # Octonions(AA). return self.entry_algebra().from_vector(e_ij.to_vector()) - return sum( (self.monomial( (i,j, convert(entries[i][j])) ) - for i in range(nrows) - for j in range(ncols) ), - self.zero() ) + def entry_to_element(i,j,entry): + # Convert an entry at i,j to a matrix whose only non-zero + # entry is i,j and corresponds to the entry. + p = self._entry_algebra_element_to_vector(entry) + + # We have to convert alpha_g because a priori it lives in the + # base ring of the entry algebra. + R = self.base_ring() + return self.sum_of_terms( (((i,j,g), R(alpha_g)) + for (alpha_g, g) + in zip(p, self.entry_algebra_gens()) ), + distinct=True) + + return self.sum( entry_to_element(i,j,entries[i][j]) + for j in range(ncols) + for i in range(nrows) ) + def _element_constructor_(self, elt): if elt in self: