Hi Nathann, > For Linear Programming, I need to create plenty of symbolic variables > which I use to represent linear functions.... To do it, I use the > class InfinitePolynomialRing which lets me create them easily ( and it > is really needed, as my colleagues often have to create Linear > Programs using 1000~2000 variables. This is not a problem for the > solvers, but Sage does not like it : > To understand my problem, just try this code : > > X.<x> = InfinitePolynomialRing(RR) > sum([x[i] for i in range(200)]) > > Don't you think it is a bit long just to generate a sum ? I have to > admit I do not know how this class is coded, and the slowness may be > required for applications different from mine.. But wouldn't there be > a way to speed this up ? If not, do you know of any way to generate > many symbolic variables ( they do not need to be polynomial, just > linear in my case ) ?
This is indeed a problem. I think I know the cause... Each time a new variable is created, the ring itself is somehow changed. Therefore for each new variable in your sum, there is a big computation which convert the former sum to the new ring. Though this could be improved by using a similar trick than doubling the size of a list when appending element, I'm not sure that's what we want. In the mean time. I have the following workaround: Just start by declaring your last variable: ---------------------------------------------------------------------- | Sage Version 4.2, Release Date: 2009-10-24 | | Type notebook() for the GUI, and license() for information. | ---------------------------------------------------------------------- Loading Sage library. Current Mercurial branch is: combinat sage: X.<x> = InfinitePolynomialRing(RR) sage: x[1000] x1000 sage: time sum([x[i] for i in range(1000)]) CPU times: user 0.66 s, sys: 0.00 s, total: 0.66 s Wall time: 0.66 s [...] Cheers, Florent -- 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
