#5520: [with patch; positive review] implement Pizer's algorithm for computing
Brandt Modules and Brandt Matrices
---------------------------+------------------------------------------------
Reporter: was | Owner: craigcitro
Type: enhancement | Status: new
Priority: major | Milestone: sage-3.4.1
Component: modular forms | Keywords:
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Comment(by tornaria):
For the record (kind of unrelated), the following line:
{{{
matrix(QQ,2,2,[1,0,0,1])._pari_().qfrep(10)
}}}
reproduces the need for using {{{gdiv}}} and {{{gtomat}}}. Indeed, if
{{{gtomat}}} is removed(for this case in
{{{sage/matrix/matrix_rational_dense.pyx}}}), then pari raises
{{{
PariError: (8)
}}}
OTOH, if {{{gtomat}}} is used, but {{{gdiv}}} is replaced by {{{mkfrac}}},
then pari raises
{{{
PariError: incorrect type (20)
}}}
The latter makes a lot of sense, since {{{qfrep}}} indeed expects a matrix
with ''integer'' coefficients, but we are passing a matrix with rational
coefficients, which just happen to be of the form {{{a/1}}}. Now, of
course, when calling {{{mkfrac(a,1)}}}, we obtain a fraction, but when
calling {{{gdi(a,1)}}} we get {{{a}}} as a "t_INT".
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/5520#comment:26>
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