On Monday, July 15, 2013 3:09:29 PM UTC-7, Volker Braun wrote: > > That is correct. The change_ring() methods in Sage return a new object and > do _not_ modify the original object:
Fair enough. I think we have found a true coercion problem involving finite fields & toric varieties, though. This one arises when constructing anticanonical hypersurfaces in a Fano toric variety with coefficients in a finite field. Let's make a smooth Fano toric variety over a finite field of non-prime order: o = lattice_polytope.octahedron(3) cube = o.polar() VRes = CPRFanoToricVariety(Delta_polar=cube, coordinate_points="all") field = GF(5^2, 'a') X=VRes.change_ring(field) Then let's define a hypersurface with coefficients specified by a list of elements in our field: hyp = X.anticanonical_hypersurface(monomial_points="vertices+origin", coefficients=[field(1),field(1),field(1),field(1),field(1),field(1),field(3)]) This raises a type error: Error in lines 6-6 Traceback (most recent call last): File "/mnt/home/7tQIE6sJ/.sagemathcloud/sage_server.py", line 494, in execute exec compile(block+'\n', '', 'single') in namespace, locals File "", line 1, in <module> File "/mnt/home/7tQIE6sJ/sage-5.10-linux-64bit-ubuntu_12.04.2_lts-x86_64-Linux/local/lib/python2.7/site-packages/sage/schemes/toric/fano_variety.py", line 905, in anticanonical_hypersurface return AnticanonicalHypersurface(self, **kwds) File "/mnt/home/7tQIE6sJ/sage-5.10-linux-64bit-ubuntu_12.04.2_lts-x86_64-Linux/local/lib/python2.7/site-packages/sage/schemes/toric/fano_variety.py", line 1438, in __init__ for m, coef in zip(monomial_points, coefficients)) File "/mnt/home/7tQIE6sJ/sage-5.10-linux-64bit-ubuntu_12.04.2_lts-x86_64-Linux/local/lib/python2.7/site-packages/sage/schemes/toric/fano_variety.py", line 1432, in <genexpr> coefficients = (F(SR(coef)) for coef in coefficients) File "parent.pyx", line 961, in sage.structure.parent.Parent.__call__ (sage/structure/parent.c:8136) File "coerce_maps.pyx", line 82, in sage.structure.coerce_maps.DefaultConvertMap_unique._call_ (sage/structure/coerce_maps.c:3856) File "coerce_maps.pyx", line 77, in sage.structure.coerce_maps.DefaultConvertMap_unique._call_ (sage/structure/coerce_maps.c:3757) File "/mnt/home/7tQIE6sJ/sage-5.10-linux-64bit-ubuntu_12.04.2_lts-x86_64-Linux/local/lib/python2.7/site-packages/sage/rings/finite_rings/finite_field_givaro.py", line 362, in _element_constructor_ return self._cache.element_from_data(e) File "element_givaro.pyx", line 377, in sage.rings.finite_rings.element_givaro.Cache_givaro.element_from_data (sage/rings/finite_rings/element_givaro.cpp:6428) File "element_givaro.pyx", line 490, in sage.rings.finite_rings.element_givaro.Cache_givaro.element_from_data (sage/rings/finite_rings/element_givaro.cpp:6126) TypeError: unable to coerce We suspect the problematic coercion comes from this line in the AnticanonicalHypersurface class: # Direct conversion "a/b" to F does not work in Sage-4.6.alpha3, # so we go through SR, even though it is quite slow. coefficients = (F(SR(coef)) for coef in coefficients) --Ursula. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To post to this group, send email to sage-devel@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel. For more options, visit https://groups.google.com/groups/opt_out.
