Agreed, unless you need extended precision for some reason. Using Gauss elimination with MPFR-matrices is still a bug.
On Friday, October 26, 2012 2:17:43 PM UTC+1, jason wrote: > > On 10/26/12 6:25 AM, Volker Braun wrote: > > The matrix is over RR (MPFR software floats). M.change_ring(RDF).det() > > gives the right answer. > > > > There is no special det() implementation for RR, we compute the > > Hessenberg form and from that characteristic polynomial. Sage uses > > Gaussian elimination to compute the Hessenberg form, and this is known > > to be numerically unstable in unfavorable cases > > (http://www.jstor.org/stable/2004967). I guess your matrix is one of > > these cases; there is no overflow, its a numerical instability. > > > > > > > Yep. If you're doing computations with numerical matrices, you should > always use RDF or CDF matrices. In this case, RDF/CDF matrices use LU > factorization and then compute the determinant from that, using the > scipy.linalg.determinant function (which in turn uses LAPACK). > > Thanks, > > Jason > > > > -- You received this message because you are subscribed to the Google Groups "sage-devel" group. 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. Visit this group at http://groups.google.com/group/sage-devel?hl=en.
