From 4f81ab7d6a598efe9a672399cfb8d43e85d7a6c9 Mon Sep 17 00:00:00 2001 From: Sebastian Spindler Date: Thu, 21 Mar 2024 22:08:38 +0100 Subject: [PATCH] Corrections in `.normalize_basis_at_p` ... ... and additional fix in `.maximal_order()`. --- .../algebras/quatalg/quaternion_algebra.py | 45 ++++++++++++++++--- 1 file changed, 38 insertions(+), 7 deletions(-) diff --git a/src/sage/algebras/quatalg/quaternion_algebra.py b/src/sage/algebras/quatalg/quaternion_algebra.py index 849a5bdd727..e83b3e39aa2 100644 --- a/src/sage/algebras/quatalg/quaternion_algebra.py +++ b/src/sage/algebras/quatalg/quaternion_algebra.py @@ -755,8 +755,7 @@ def maximal_order(self, take_shortcuts=True): sage: for d in ( m for m in range(1, 750) if is_squarefree(m) ): # long time (3s) ....: A = QuaternionAlgebra(d) - ....: R = A.maximal_order(take_shortcuts=False) - ....: assert A.discriminant() == R.discriminant() + ....: assert A.maximal_order(take_shortcuts=False).is_maximal() We do not support number fields other than the rationals yet:: @@ -766,6 +765,17 @@ def maximal_order(self, take_shortcuts=True): ... NotImplementedError: maximal order only implemented for rational quaternion algebras + + TESTS: + + We check that the first part of :issue:`37217` is fixed:: + + sage: invars = [(-292, -732), (-48, -564), (-436, -768), (-752, -708), (885, 545), + ....: (411, -710), (-411, 593), (805, -591), (-921, 353), (409, 96), + ....: (394, 873), (353, -722), (730, 830), (-466, -427), (-213, -630), + ....: (-511, 608), (493, 880), (105, -709), (-213, 530), (97, 745)] + sage: all(QuaternionAlgebra(a, b).maximal_order().is_maximal() for (a,b) in invars) + True """ if self.base_ring() != QQ: raise NotImplementedError("maximal order only implemented for rational quaternion algebras") @@ -819,7 +829,8 @@ def maximal_order(self, take_shortcuts=True): # For each prime at which R is not yet maximal, make it bigger for p, _ in d_R.factor(): e = R.basis() - while self.quaternion_order(e).discriminant().valuation(p) > d_A.valuation(p): + disc = self.quaternion_order(e).discriminant() + while disc.valuation(p) > d_A.valuation(p): # Compute a normalized basis at p f = normalize_basis_at_p(list(e), p) @@ -896,6 +907,16 @@ def maximal_order(self, take_shortcuts=True): # be an order). We will join them all together at the end e = e_n + # Since e might not define an order at this point, we need to manually + # calculate the updated discriminant + L = [] + for x in e: + MM = [] + for y in e: + MM.append(x.pair(y)) + L.append(MM) + disc = (MatrixSpace(QQ, 4, 4)(L)).determinant().sqrt() + e_new_gens.extend(e[1:]) e_new = basis_for_quaternion_lattice(list(R.basis()) + e_new_gens, reverse=True) @@ -3529,7 +3550,18 @@ def normalize_basis_at_p(e, p, B=QuaternionAlgebraElement_abstract.pair): sage: e = [A(1), k, j, 1/2 + 1/2*i + 1/2*j + 1/2*k] sage: normalize_basis_at_p(e, 2) [(1, 0), (1/2 + 1/2*i + 1/2*j + 1/2*k, 0), (-34/105*i - 463/735*j + 71/105*k, 1), - (-34/105*i - 463/735*j + 71/105*k, 1)] + (1/7*i - 8/49*j + 1/7*k, 1)] + + TESTS: + + We check that the second part of :issue:`37217` is fixed:: + + sage: A. = QuaternionAlgebra(-1,-7) + sage: e = [A(1), k, j, 1/2 + 1/2*i + 1/2*j + 1/2*k] + sage: e_norm = normalize_basis_at_p(e, 2) + sage: V = QQ**4 + sage: V.span([V(x.coefficient_tuple()) for (x,_) in e_norm]).dimension() + 4 """ N = len(e) @@ -3577,8 +3609,7 @@ def normalize_basis_at_p(e, p, B=QuaternionAlgebraElement_abstract.pair): # Ensures that (B(f0,f0)/2).valuation(p) <= B(f0,f1).valuation(p) if B(f0, f1).valuation(p) + 1 < B(f0, f0).valuation(p): - f0 += f1 - f1 = f0 + f0, f1 = f0 + f1, f0 # Make remaining vectors orthogonal to span of f0, f1 e[min_m] = e[0] @@ -3591,7 +3622,7 @@ def normalize_basis_at_p(e, p, B=QuaternionAlgebraElement_abstract.pair): tu = [(B01 * B(f1, e[l]) - B11 * B(f0, e[l]), B01 * B(f0, e[l]) - B00 * B(f1, e[l])) for l in range(2, N)] - e[2:n] = [e[l] + tu[l-2][0]/d * f0 + tu[l-2][1]/d * f1 for l in range(2, N)] + e[2:N] = [e[l] + tu[l-2][0]/d * f0 + tu[l-2][1]/d * f1 for l in range(2, N)] # Recursively normalize remaining vectors f = normalize_basis_at_p(e[2:N], p)