On Wednesday, July 10, 2013 10:14:52 AM UTC-7, John H Palmieri wrote: > > > > On Wednesday, July 10, 2013 9:31:25 AM UTC-7, Peter Mueller wrote: >> >> In the following code the computation seems to run forever, even hitting >> Ctrl-C doesn't stop that. >> >> k.<b,c> = QQ[] >> l = k.fraction_field() >> r.<x> = l[] >> A = 2*(x^4+x^40)+b*(x^8+x^36)+c*(x^12+x^32) >> B = A.subs(1/x) >> >> If I drop the factor 2* in A=..., then I instantly get the correct >> result. I'm running Sage 5.10. >> >> I know that factorizations of multivariate polynomials always has been a >> mess in Sage, but I'm surprised to see that even a trivial formal >> computation doesn't work reliably. >> > > I don't know why this happens, but a workaround: >
Another workaround: don't use the fraction field l, so replace l = k.fraction_field() r.<x> = l[] with r.<x> = k[] I think that working in iterated fraction fields (where you've first inverted b, c, etc., and then by using 1/x, you've inverted x, etc.) is very slow. You could also do r.<x> = k[] s = r.fraction_field() A = s(A) so now A is in the fraction field of QQ[b,c,x]. Then A.subs(x=1/x) works. -- John -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/groups/opt_out.
