On Thu, Dec 17, 2009 at 7:16 PM, Sebastian Pancratz <[email protected]> wrote: > Dear William, > > This is just a very brief reply (before going to bed, it's past 3am here). > I've added the bug report as ticket #7730.
http://trac.sagemath.org/sage_trac/ticket/7730 > After I've had a quick look at the problem, it seems it's caused by the > computation of the Hessenberg form. In fact, supplying the choice > "algorithm='df'" would allow the person who submitted the bug report to carry > out the computation quickly. Just in case that person is interested (I am > not quite sure what the arrangement for replying to him is, in any case, I > think for me it's more appropriate to reply to you): > > Computation of det by minors: 2.15s > Computation of det using the division-free algorithm: 3.87microseconds > Computation of inverse: 71.6ms > > Oh, and the output in either case for the determinant is x1^2*x4^2*x5^2*x6^2 > + x0^2*x2^2*x3^2*x7^2, which is different from the bug report. (It looks > like the powers of two were omitted in the bug report.) > > While I am not all that familiar with the Hessenberg form computation, I am > happy to look at it in the next few days --- it seems something that is used > that often shouldn't be broken. > Thanks! I think I implemented Hessenberg form long, long ago following H. Cohen's book.... The generic algorithm is fine, so something must go wrong/weird in the special case under consideration. William -- To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
