From: Michael Orlitzky Date: Sat, 27 Feb 2021 23:27:26 +0000 (-0500) Subject: eja: add a deep change_ring() utility function. X-Git-Url: https://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=2108ec57e32e5417f92c4ccbff9df6fdad8a819d;p=sage.d.git eja: add a deep change_ring() utility function. --- diff --git a/mjo/eja/eja_utils.py b/mjo/eja/eja_utils.py index 832dcef..81b5634 100644 --- a/mjo/eja/eja_utils.py +++ b/mjo/eja/eja_utils.py @@ -2,6 +2,57 @@ from sage.functions.other import sqrt from sage.matrix.constructor import matrix from sage.modules.free_module_element import vector +def _change_ring(x, R): + r""" + Change the ring of a vector, matrix, or a cartesian product of + those things. + + SETUP:: + + sage: from mjo.eja.eja_utils import _change_ring + + EXAMPLES:: + + sage: v = vector(QQ, (1,2,3)) + sage: m = matrix(QQ, [[1,2],[3,4]]) + sage: _change_ring(v, RDF) + (1.0, 2.0, 3.0) + sage: _change_ring(m, RDF) + [1.0 2.0] + [3.0 4.0] + sage: _change_ring((v,m), RDF) + ( + [1.0 2.0] + (1.0, 2.0, 3.0), [3.0 4.0] + ) + sage: V1 = cartesian_product([v.parent(), v.parent()]) + sage: V = cartesian_product([v.parent(), V1]) + sage: V((v, (v, v))) + ((1, 2, 3), ((1, 2, 3), (1, 2, 3))) + sage: _change_ring(V((v, (v, v))), RDF) + ((1.0, 2.0, 3.0), ((1.0, 2.0, 3.0), (1.0, 2.0, 3.0))) + + """ + try: + return x.change_ring(R) + except AttributeError: + try: + from sage.categories.sets_cat import cartesian_product + if hasattr(x, 'element_class'): + # x is a parent and we're in a recursive call. + return cartesian_product( [_change_ring(x_i, R) + for x_i in x.cartesian_factors()] ) + else: + # x is an element, and we want to change the ring + # of its parent. + P = x.parent() + Q = cartesian_product( [_change_ring(P_i, R) + for P_i in P.cartesian_factors()] ) + return Q(x) + except AttributeError: + # No parent for x + return x.__class__( _change_ring(x_i, R) for x_i in x ) + def _scale(x, alpha): r""" Scale the vector, matrix, or cartesian-product-of-those-things