On Jun 4, 2009, at 8:53 PM, Jason Grout wrote: > Robert Bradshaw wrote: >> On Jun 4, 2009, at 5:48 PM, Craig Citro wrote: >> >>>>> Should this be changed so that m.change_ring(R) always returns a >>>>> copy? >>>> Yes, I think so. >>>> >>> +1 >> >> I'd say No. I think change_ring should be fast when it's already the >> right ring, it shouldn't be used for making copies (unless >> necessary). Perhaps it could take an optional copy parameter. > > How do you generally use the matrix after you call change_ring()? It > seems like the normal thing to do would be to change the matrix in > some > way. In that case, it is a huge bonus to have consistency between > returning the original object and returning a copy.
I usually use change_ring on polynomials, after which I extract coefficients/find roots/factor/etc. It's also nice to change the ring to be over a fraction field (i.e. M.change_ring(M.base_ring ().fraction_field())) before taking the echelon form. In general I view X.change_ring(R) as shorthand for X.parent ().change_ring(R)(X), and given a parent R, R(x) generally returns x if x is already an element of R. - Robert --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to sage-devel-unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
