Hi,
I think this is a bug. Solving x == y mod 3 works fine:
sage: var('x,y')
(x, y)
sage: solve_mod([x == y], 3)
[(0, 0), (1, 1), (2, 2)]
But solving mod 2 blows up:
sage: solve_mod([x == y], 2)
---------------------------------------------------------------------------
<type 'exceptions.TypeError'> Traceback (most recent call last)
/home/carlo/work/sagestuff/<ipython console> in <module>()
/home/carlo/sage/local/lib/python2.5/site-packages/sage/calculus/equations.py
in solve_mod(eqns, modulus)
1339 S = MPolynomialRing(R, len(vars), vars)
1340 eqns_mod = [S(eq) if is_SymbolicExpression(eq) else \
-> 1341 S(eq.lhs() - eq.rhs()) for eq in eqns]
1342
1343 ans = []
/home/carlo/sage/local/lib/python2.5/site-packages/sage/rings/polynomial/multi_polynomial_ring.py
in __call__(self, x, check)
380
381 elif hasattr(x, '_polynomial_'):
--> 382 return x._polynomial_(self)
383
384 elif isinstance(x, str) and x in self.variable_names():
/home/carlo/sage/local/lib/python2.5/site-packages/sage/calculus/calculus.py
in _polynomial_(self, R)
1809 if len(sub) == 0:
1810 try:
-> 1811 return R(B(self))
1812 except TypeError:
1813 if len(vars) == 1:
/home/carlo/sage/local/lib/python2.5/site-packages/sage/rings/integer_mod_ring.py
in __call__(self, x)
574 def __call__(self, x):
575 try:
--> 576 return integer_mod.IntegerMod(self, x)
577 except (NotImplementedError, PariError):
578 return TypeError, "error coercing to finite field"
/home/carlo/work/sagestuff/integer_mod.pyx in
sage.rings.integer_mod.IntegerMod (sage/rings/integer_mod.c:1731)()
/home/carlo/work/sagestuff/integer_mod.pyx in
sage.rings.integer_mod.IntegerMod_int.__init__
(sage/rings/integer_mod.c:10153)()
/home/carlo/work/sagestuff/integer_ring.pyx in
sage.rings.integer_ring.IntegerRing_class.__call__
(sage/rings/integer_ring.c:4473)()
<type 'exceptions.TypeError'>: unable to convert x (=x - y) to an integer
Any ideas?
--
Carlo Hamalainen
http://carlo-hamalainen.net
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