Hi Martin, hi Pierre! On Oct 20, 11:25 am, Martin Albrecht <m...@informatik.uni-bremen.de> wrote: > > speaking of shorthands, does SAGE have a ready-made function that > > computes the kernel of a ring map from a quotient of a polynomial ring > > to another such quotient ? (straightforward groebner basis computation > > again) > > I don't think so but it should be relatively easy to add (hint, hint :)) > > First, I'd check whether Singular has such a function and wrap that.
There are Singular functions "kernel" and "preimage". They do not work in graded-commutative polynomial rings (which is what I'd need in my applications), but commutatively they work. However, I am not sure if it is efficient to use these commands often. Suppose f is a map from basering to some other ring R, and I, J are ideals in R. Then, preimage(R,f,I) computes the preimage of I under f. I guess internally some Groebner basis computation is done. When you then do preimage(R,f,J), I wonder if the same Groebner basis computation is repeated, or if the first result was cached. Can some Singular expert answer whether "preimage" does caching of internal computations? If not, it might be worth while to re-implement it in libsingular. Cheers, Simon --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
