#13878: Fix failing assertion in linbox/matrix/permutation-matrix.h
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Reporter: SimonKing | Owner: jason, was
Type: defect | Status: new
Priority: major | Milestone: sage-5.6
Component: linear algebra | Resolution:
Keywords: debug, linbox, assertion | Work issues:
Report Upstream: N/A | Reviewers:
Authors: | Merged in:
Dependencies: | Stopgaps:
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Comment (by nbruin):
Offending code is this:
{{{
cdef inline linbox_echelonize_efd(celement modulus, celement* entries,
Py_ssize_t nrows, Py_ssize_t ncols):
cdef ModField *F = new ModField(<long>modulus)
cdef EchelonFormDomain *EF = new EchelonFormDomain(F[0])
cdef BlasMatrix *A = new BlasMatrix(F[0], <uint64_t>nrows,
<uint64_t>ncols)
cdef BlasMatrix *E = new BlasMatrix(F[0], <uint64_t>nrows,
<uint64_t>ncols)
cdef Py_ssize_t i,j
# TODO: can we avoid this copy?
for i in range(nrows):
for j in range(ncols):
A.setEntry(i, j, <ModFieldElement>entries[i*ncols+j])
cdef int r = EF.rowReducedEchelon(E[0], A[0])
for i in range(nrows):
for j in range(ncols):
entries[i*ncols+j] = <celement>E.getEntry(i,j)
cdef Py_ssize_t ii = 0
cdef list pivots = []
for i in range(r):
for j in range(ii,ncols):
if entries[i*ncols+j] == 1:
pivots.append(j)
ii = j+1
break
del F, A, E, EF
return r, pivots
}}}
This gets called with `nrows=0`, so `A` does not get initialized with
anything (there's noting to set!). I suppose linbox should handle such an
edge case, but I haven't checked their doc to see if they exclude it as
valid. Obviously, it's easy to special case this degeneracy: If `nrows=0`
then we should return 0,[]. It's probably worthwhile to fix this, but I'm
pretty sure this is not a source for bugs otherwise.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13878#comment:4>
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