X-Git-Url: http://gitweb.michael.orlitzky.com/?a=blobdiff_plain;f=mjo%2Feja%2Feja_utils.py;h=d4e9990ecc6749057905d3b1d5ac700bd34cdc71;hb=8f3ba1d9473195c1cbafe967a127800d90fde3ee;hp=803ec636520515543c873ecc59669475a0048a3c;hpb=21fa036e86711c6c28b6d89af2b1bfe4ceb24b29;p=sage.d.git diff --git a/mjo/eja/eja_utils.py b/mjo/eja/eja_utils.py index 803ec63..d4e9990 100644 --- a/mjo/eja/eja_utils.py +++ b/mjo/eja/eja_utils.py @@ -2,19 +2,122 @@ from sage.functions.other import sqrt from sage.matrix.constructor import matrix from sage.modules.free_module_element import vector +def _scale(x, alpha): + r""" + Scale the vector, matrix, or cartesian-product-of-those-things + ``x`` by ``alpha``. + + This works around the inability to scale certain elements of + Cartesian product spaces, as reported in + + https://trac.sagemath.org/ticket/31435 + + ..WARNING: + + This will do the wrong thing if you feed it a tuple or list. + + SETUP:: + + sage: from mjo.eja.eja_utils import _scale + + EXAMPLES:: + + sage: v = vector(QQ, (1,2,3)) + sage: _scale(v,2) + (2, 4, 6) + sage: m = matrix(QQ, [[1,2],[3,4]]) + sage: M = cartesian_product([m.parent(), m.parent()]) + sage: _scale(M((m,m)), 2) + ([2 4] + [6 8], [2 4] + [6 8]) + + """ + if hasattr(x, 'cartesian_factors'): + P = x.parent() + return P(tuple( _scale(x_i, alpha) + for x_i in x.cartesian_factors() )) + else: + return x*alpha + + def _all2list(x): r""" Flatten a vector, matrix, or cartesian product of those things into a long list. + + If the entries of the matrix themselves belong to a real vector + space (such as the complex numbers which can be thought of as + pairs of real numbers), they will also be expanded in vector form + and flattened into the list. + + SETUP:: + + sage: from mjo.eja.eja_utils import _all2list + sage: from mjo.octonions import Octonions, OctonionMatrixAlgebra + + EXAMPLES:: + + sage: _all2list([[1]]) + [1] + + :: + + sage: V1 = VectorSpace(QQ,2) + sage: V2 = MatrixSpace(QQ,2) + sage: x1 = V1([1,1]) + sage: x2 = V1([1,-1]) + sage: y1 = V2.one() + sage: y2 = V2([0,1,1,0]) + sage: _all2list((x1,y1)) + [1, 1, 1, 0, 0, 1] + sage: _all2list((x2,y2)) + [1, -1, 0, 1, 1, 0] + sage: M = cartesian_product([V1,V2]) + sage: _all2list(M((x1,y1))) + [1, 1, 1, 0, 0, 1] + sage: _all2list(M((x2,y2))) + [1, -1, 0, 1, 1, 0] + + :: + + sage: _all2list(Octonions().one()) + [1, 0, 0, 0, 0, 0, 0, 0] + sage: _all2list(OctonionMatrixAlgebra(1).one()) + [1, 0, 0, 0, 0, 0, 0, 0] + + :: + + sage: V1 = VectorSpace(QQ,2) + sage: V2 = OctonionMatrixAlgebra(1,field=QQ) + sage: C = cartesian_product([V1,V2]) + sage: x1 = V1([3,4]) + sage: y1 = V2.one() + sage: _all2list(C( (x1,y1) )) + [3, 4, 1, 0, 0, 0, 0, 0, 0, 0] + """ - if hasattr(x, 'list'): - # Easy case... - return x.list() - else: - # But what if it's a tuple or something else? This has to - # handle cartesian products of cartesian products, too; that's - # why it's recursive. - return sum( map(_all2list,x), [] ) + if hasattr(x, 'to_vector'): + # This works on matrices of e.g. octonions directly, without + # first needing to convert them to a list of octonions and + # then recursing down into the list. It also avoids the wonky + # list(x) when x is an element of a CFM. I don't know what it + # returns but it aint the coordinates. This will fall through + # to the iterable case the next time around. + return _all2list(x.to_vector()) + + try: + xl = list(x) + except TypeError: # x is not iterable + return [x] + + if xl == [x]: + # Avoid the retardation of list(QQ(1)) == [1]. + return [x] + + return sum(list( map(_all2list, xl) ), []) + + def _mat2vec(m): return vector(m.base_ring(), m.list()) @@ -92,6 +195,28 @@ def gram_schmidt(v, inner_product=None): [0 0], [1/2*sqrt(2) 0], [0 1] ] + It even works on Cartesian product spaces whose factors are vector + or matrix spaces:: + + sage: V1 = VectorSpace(AA,2) + sage: V2 = MatrixSpace(AA,2) + sage: M = cartesian_product([V1,V2]) + sage: x1 = V1([1,1]) + sage: x2 = V1([1,-1]) + sage: y1 = V2.one() + sage: y2 = V2([0,1,1,0]) + sage: z1 = M((x1,y1)) + sage: z2 = M((x2,y2)) + sage: def ip(a,b): + ....: return a[0].inner_product(b[0]) + (a[1]*b[1]).trace() + sage: U = gram_schmidt([z1,z2], inner_product=ip) + sage: ip(U[0],U[1]) + 0 + sage: ip(U[0],U[0]) + 1 + sage: ip(U[1],U[1]) + 1 + TESTS: Ensure that zero vectors don't get in the way:: @@ -102,11 +227,17 @@ def gram_schmidt(v, inner_product=None): sage: v = [v1,v2,v3] sage: len(gram_schmidt(v)) == 2 True - """ if inner_product is None: inner_product = lambda x,y: x.inner_product(y) - norm = lambda x: inner_product(x,x).sqrt() + def norm(x): + ip = inner_product(x,x) + # Don't expand the given field; the inner-product's codomain + # is already correct. For example QQ(2).sqrt() returns sqrt(2) + # in SR, and that will give you weird errors about symbolics + # when what's really going wrong is that you're trying to + # orthonormalize in QQ. + return ip.parent()(ip.sqrt()) v = list(v) # make a copy, don't clobber the input @@ -119,18 +250,16 @@ def gram_schmidt(v, inner_product=None): R = v[0].base_ring() - # Define a scaling operation that can be used on tuples. - # Oh and our "zero" needs to belong to the right space. - scale = lambda x,alpha: x*alpha + # Our "zero" needs to belong to the right space for sum() to work. zero = v[0].parent().zero() - if hasattr(v[0], 'cartesian_factors'): - P = v[0].parent() - scale = lambda x,alpha: P(tuple( x_i*alpha - for x_i in x.cartesian_factors() )) + sc = lambda x,a: a*x + if hasattr(v[0], 'cartesian_factors'): + # Only use the slow implementation if necessary. + sc = _scale def proj(x,y): - return scale(x, (inner_product(x,y)/inner_product(x,x))) + return sc(x, (inner_product(x,y)/inner_product(x,x))) # First orthogonalize... for i in range(1,len(v)): @@ -147,6 +276,6 @@ def gram_schmidt(v, inner_product=None): # them here because then our subalgebra would have a bigger field # than the superalgebra. for i in range(len(v)): - v[i] = scale(v[i], ~norm(v[i])) + v[i] = sc(v[i], ~norm(v[i])) return v