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Simplify matrix construction in btquotient #40239

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Simplify matrix construction in btquotient #40239

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c444bb2
simplify matrix construction
Eloitor Jun 9, 2025
18d5c81
simplify matrix construction
Eloitor Jun 9, 2025
81ad425
simplify matrix construction
Eloitor Jun 10, 2025
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14 changes: 5 additions & 9 deletions src/sage/modular/btquotients/btquotient.py
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Original file line number Diff line number Diff line change
Expand Up @@ -45,6 +45,7 @@
from sage.interfaces.magma import magma
from sage.matrix.constructor import Matrix
from sage.matrix.matrix_space import MatrixSpace
from sage.matrix.special import column_matrix
from sage.misc.cachefunc import cached_method
from sage.misc.latex import latex
from sage.misc.lazy_attribute import lazy_attribute
Expand Down Expand Up @@ -2273,9 +2274,7 @@ def _compute_embedding_matrix(self, prec, force_computation=False):
else:
phi = self._local_splitting_map(prec)
B = self.get_eichler_order_basis()
return Matrix(Zmod(self._p ** prec), 4, 4,
[phi(B[kk])[ii, jj] for ii in range(2)
for jj in range(2) for kk in range(4)])
return column_matrix(Zmod(self._p ** prec), 4, 4, [phi(b).list() for b in B])

@cached_method
def get_extra_embedding_matrices(self):
Expand Down Expand Up @@ -2441,12 +2440,10 @@ def get_embedding_matrix(self, prec=None, exact=False):
verbose('self._prec = %s, prec = %s' % (self._prec, prec))
Iotamod = self._compute_embedding_matrix(prec)
self._Iotainv_lift = Iotamod.inverse().lift()
self._Iota = Matrix(self._R, 4, 4, [Iotamod[ii, jj]
for ii in range(4)
for jj in range(4)])
self._Iota = Matrix(self._R, Iotamod)

self._prec = prec
self._Iotainv = self._Mat_44([self._Iotainv_lift[ii, jj] % self._pN for ii in range(4) for jj in range(4)])
self._Iotainv = self._Mat_44(self._Iotainv_lift.apply_map(lambda x: x % self._pN))
return self._Iota

def embed_quaternion(self, g, exact=False, prec=None):
Expand Down Expand Up @@ -3153,8 +3150,7 @@ def _find_lattice(self, v1, v2, as_edges, m):
v1adj = v1.adjugate()
R = self._Mat_44
vecM = [v2 * X[ii] * v1adj for ii in range(4)]
M = self._Iotainv * R([[vecM[ii][jj, kk] for ii in range(4)]
for jj in range(2) for kk in range(2)])
M = self._Iotainv * column_matrix(4, 4, [m.list() for m in vecM])
M = M.augment(R(self._pN)).transpose()
E = M.echelon_form().submatrix(0, 0, 4, 4)
Et = E.transpose()
Expand Down
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