That is correct. The change_ring() methods in Sage return a new object and do _not_ modify the original object:
sage: x = toric_varieties.P2() sage: x.base_ring() Rational Field sage: x.change_ring(GF(3)).base_ring() Finite Field of size 3 sage: x.base_ring() Rational Field Similar: sage: R = PolynomialRing(QQ, 'x') sage: R.base_ring() Rational Field sage: R.change_ring(GF(3)) Univariate Polynomial Ring in x over Finite Field of size 3 sage: R.base_ring() Rational Field On Monday, July 15, 2013 5:57:21 PM UTC-4, Ursula wrote: > > When you change the ring for a toric variety, that ring change does not > propagate to the affine patches on the toric variety. > > Here's an example: > > o = lattice_polytope.octahedron(3) > cube = o.polar() > VRes = CPRFanoToricVariety(Delta_polar=cube, coordinate_points="all") > q =5^2 > field = GF(q, 'a') > VRes.change_ring(field) > patch = VRes.affine_patch(0) > em = patch.embedding_morphism() > emDomain = em.domain() > emDomain.base_ring() > > This returns > > Rational Field. > > VRes is a 3-dimensional toric variety, so emDomain should be field^3. If > you try to map an element of field^3 into VRes using the patch embedding > morphism, you get a type error due to a failed coercion. > > For example, > > em(emDomain(field(1), field(1), field(1))) > > returns > > TypeError: Unable to coerce 1 (<type > 'sage.rings.finite_rings.element_givaro.FiniteField_givaroElement'>) to > Rational > > --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.
