Indeed, calling previous_prime(p) with p=2 does not sound like a good
idea :-) The following is very suspicious to me
~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/matrix/misc.pyx
in sage.matrix.misc.matrix_rational_echelon_form_multimodular
(build/cythonized/sage/matrix/misc.c:7147)()
375 verbose("Excluding this prime (bad pivots).",
caller_name="multimod echelon")
376 t = verbose("time for pivot compare", t, level=2,
caller_name="multimod echelon")
--> 377 p = previous_prime(p)
Vincent
On Fri, 29 Jul 2022 at 16:07, Trevor Karn <trevor.k.k...@gmail.com> wrote:
>
> Hi all,
>
> I'm working on trac ticket https://trac.sagemath.org/ticket/34138 and during
> some testing on commit b3ef1f7 got an error that I don't understand. In
> implementing the F4 algorithm there is a computation of matrix RREF. During
> that step, on the "gametwo7" example of
> https://web.archive.org/web/20181129231728/http://www.cecm.sfu.ca/~rpearcea/polsys.txt,
> I get the error below. It looks like the error is occurring in the matrix
> row reduction. Does this seem like a bug with the Groebner basis code or with
> the matrix code?
>
> Thanks so much!
>
> Best,
> Trevor
>
> ---------------------------------------------------------------------------
>
> ValueError Traceback (most recent call last)
>
> <ipython-input-11-92ee538afd06> in <module>
>
> ----> 1 cProfile.runctx('I.groebner_basis()', globals(), locals(),
> 'profile.prof')
>
>
> /usr/local/Cellar/python@3.9/3.9.9/Frameworks/Python.framework/Versions/3.9/lib/python3.9/cProfile.py
> in runctx(statement, globals, locals, filename, sort)
>
> 17
>
> 18 def runctx(statement, globals, locals, filename=None, sort=-1):
>
> ---> 19 return _pyprofile._Utils(Profile).runctx(statement, globals,
> locals,
>
> 20 filename, sort)
>
> 21
>
>
> /usr/local/Cellar/python@3.9/3.9.9/Frameworks/Python.framework/Versions/3.9/lib/python3.9/profile.py
> in runctx(self, statement, globals, locals, filename, sort)
>
> 60 prof = self.profiler()
>
> 61 try:
>
> ---> 62 prof.runctx(statement, globals, locals)
>
> 63 except SystemExit:
>
> 64 pass
>
>
> /usr/local/Cellar/python@3.9/3.9.9/Frameworks/Python.framework/Versions/3.9/lib/python3.9/cProfile.py
> in runctx(self, cmd, globals, locals)
>
> 98 self.enable()
>
> 99 try:
>
> --> 100 exec(cmd, globals, locals)
>
> 101 finally:
>
> 102 self.disable()
>
>
> <string> in <module>
>
>
> ~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/algebras/clifford_algebra.py
> in groebner_basis(self, term_order)
>
> 2755 return self._groebner_strategy.groebner_basis
>
> 2756 self._groebner_strategy = strategy(self)
>
> -> 2757 self._groebner_strategy.compute_groebner()
>
> 2758 return self._groebner_strategy.groebner_basis
>
> 2759
>
>
> ~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/algebras/exterior_algebra_groebner.pyx
> in sage.algebras.exterior_algebra_groebner.GroebnerStrategy.compute_groebner
> (build/cythonized/sage/algebras/exterior_algebra_groebner.c:8678)()
>
> 221 while P:
>
> 222 Pp = P.pop(min(P)) # The selection: lowest lcm degree
>
> --> 223 Gp = self.reduction(Pp, G)
>
> 224 G.extend(Gp)
>
> 225 for j in range(n, len(G)):
>
>
> ~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/algebras/exterior_algebra_groebner.pyx
> in sage.algebras.exterior_algebra_groebner.GroebnerStrategy.reduction
> (build/cythonized/sage/algebras/exterior_algebra_groebner.c:7581)()
>
> 178 for m,c in (<CliffordAlgebraElement>
> f)._monomial_coefficients.items()},
>
> 179 sparse=True)
>
> --> 180 M.echelonize() # Do this in place
>
> 181 lead_supports =
> set(self.leading_supp(<CliffordAlgebraElement> f) for f in L)
>
> 182 return [self.E.element_class(self.E, {self.int_to_bitset(r -
> Integer(j)): c for j,c in M[i].iteritems()})
>
>
> ~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/matrix/matrix_rational_sparse.pyx
> in sage.matrix.matrix_rational_sparse.Matrix_rational_sparse.echelonize
> (build/cythonized/sage/matrix/matrix_rational_sparse.c:7063)()
>
> 524 self.check_mutability()
>
> 525
>
> --> 526 pivots = self._echelonize_multimodular(height_guess, proof,
> **kwds)
>
> 527
>
> 528 self.cache('in_echelon_form', True)
>
>
> ~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/matrix/matrix_rational_sparse.pyx
> in
> sage.matrix.matrix_rational_sparse.Matrix_rational_sparse._echelonize_multimodular
> (build/cythonized/sage/matrix/matrix_rational_sparse.c:7609)()
>
> 571 def _echelonize_multimodular(self, height_guess=None, proof=True,
> **kwds):
>
> 572 cdef Matrix_rational_sparse E
>
> --> 573 E, pivots = self._echelon_form_multimodular(height_guess,
> proof=proof, **kwds)
>
> 574 self.clear_cache()
>
> 575 # Swap the data of E and self (effectively moving E to self)
>
>
> ~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/matrix/matrix_rational_sparse.pyx
> in
> sage.matrix.matrix_rational_sparse.Matrix_rational_sparse._echelon_form_multimodular
> (build/cythonized/sage/matrix/matrix_rational_sparse.c:7874)()
>
> 589 from .misc import matrix_rational_echelon_form_multimodular
>
> 590 cdef Matrix E
>
> --> 591 E, pivots = matrix_rational_echelon_form_multimodular(self,
>
> 592 height_guess=height_guess,
> proof=proof)
>
> 593 E._parent = self._parent
>
>
> ~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/matrix/misc.pyx
> in sage.matrix.misc.matrix_rational_echelon_form_multimodular
> (build/cythonized/sage/matrix/misc.c:7147)()
>
> 375 verbose("Excluding this prime (bad pivots).",
> caller_name="multimod echelon")
>
> 376 t = verbose("time for pivot compare", t, level=2,
> caller_name="multimod echelon")
>
> --> 377 p = previous_prime(p)
>
> 378 # Find set of best matrices.
>
> 379 Y = []
>
>
> ~/Applications/sage/local/var/lib/sage/venv-python3.9/lib/python3.9/site-packages/sage/arith/misc.py
> in previous_prime(n)
>
> 1234 n = ZZ(n) - 1
>
> 1235 if n <= 1:
>
> -> 1236 raise ValueError("no previous prime")
>
> 1237 if n <= 3:
>
> 1238 return ZZ(n)
>
>
> ValueError: no previous prime
>
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