Re: [sage-support] Matrices and Cyclotomics
On 25/04/2012 16:45, Graham Gerrard wrote: Finding occasional inconsistencies when using matrices with cyclotomic entries, though works well most of the time... sage: s=CyclotomicField(24,'s').gen() sage: (8*s^6-1)^10 -1098715216*s^6 - 372960063 sage: xb=matrix(1,1,[8*s^6-1]) sage: xb^10 [1036922553*s^6 - 372960063] I can confirm this behaviour. Above example is trivial computation, though problem recurs in several contexts. I believe that scalar multiplication is correct and xb^10 incorrect. Yes, I've checked with Magma and you're right. Any suggestions? Sage has a special algorithm for multiplying matrices over cyclotomic fields which works modulo primes and then does a Chinese remainder to put the answer together. There is presumably a problem somewhere in this algorithm but I don't know where. A rather unpleasant workaround is to do xb.sparse_matrix()^10 Sage just uses a generic algorithm for multiplying the sparse matrices so this gives the correct answer. However, the performance probably won't be as good. Alastair -- 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
Re: [sage-support] Matrices and Cyclotomics
On Friday, April 27, 2012 6:38:50 AM UTC+8, William Stein wrote: E.g., in sage-5.0-pre15: sage: sage: s=CyclotomicField(24,'s').gen() sage: sage: (8*s^6-1)^10 -1098715216*s^6 - 372960063 sage: sage: xb=matrix(1,1,[8*s^6-1]) sage: sage: xb^10 [-1098715216*s^6 - 372960063] This statement may become false in the future, because 5.0.beta15 is still under construction. -Keshav Join us in #sagemath on irc.freenode.net ! -- 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
[sage-support] Matrices and Cyclotomics
Finding occasional inconsistencies when using matrices with cyclotomic entries, though works well most of the time... sage: s=CyclotomicField(24,'s').gen() sage: (8*s^6-1)^10 -1098715216*s^6 - 372960063 sage: xb=matrix(1,1,[8*s^6-1]) sage: xb^10 [1036922553*s^6 - 372960063] Above example is trivial computation, though problem recurs in several contexts. I believe that scalar multiplication is correct and xb^10 incorrect. Above example works OK when powers10. Any suggestions? Graham -- 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
