On 17 April 2012 08:15, P Purkayastha <ppu...@gmail.com> wrote: > Hi, > The following piece of code seems to error out: > sage: C = BinaryGolayCode() > sage: c = C[1]; c.change_ring(ZZ) # This works > (1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 1, 1, 1, 0, 0, 0, 1) > sage: c = C[20]; c.change_ring(ZZ) # This gives error > ... > TypeError: element (= [0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, > 1, 1, 0, 0, 1]) is not in free module > > The question is why does it error out on trying to change ring from GF(2) to > ZZ? I suppose it should be always possible to coerce from GF(p) to ZZ for p > prime.
My guess is that C[1] happens to be a Z-linear combination of the lifted basis vectors for C (it probably is a basis vector) but C[20] is the 20th in a list of 4096 vectors in the subspace, which is not a Z-linear combination of the lifted basis vectors. This works: sage: C.ambient_space()(C[20]).change_ring(ZZ) (0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 1) since by moving up to the ambient space we lose the condition that the vector should be a Z-linear combination of the lifted basis vectors, which it is not (it only is mod 2). John > > -- > To post to this group, send an email to sage-devel@googlegroups.com > To unsubscribe from this group, send an email to > sage-devel+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/sage-devel > URL: http://www.sagemath.org -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
