Re: Bug in symbolic inversion of matrices
- Subject: [mg2619] Re: Bug in symbolic inversion of matrices
- From: danl (Daniel Lichtblau)
- Date: Thu, 30 Nov 1995 20:58:38 -0500
- Approved: usenet@wri.com
- Distribution: local
- Newsgroups: wri.mathgroup
- Organization: Wolfram Research, Inc.
In article <49dp5g$8a6 at dragonfly.wri.com> chapman at bonnie.drea.dnd.ca (David M.F. Chapman) writes: > I have not been following this newsgroup, so I apologize if the following is > old hat: > > We have found a probable bug involving the symbolic inversion of matrices. > Up to size 6x6 works fine, but starting with 7x7, all the memory is gobbled > up and the abort calculation command does not work. Funny thing, it only > acts up when the result is printed, so it may have more to do with that > aspect than the inversion itself. I will send the annotated notebook > documenting this bug to anyone interested. (I have already sent a copy to > Wolfram Research.) > ************************************************************************** ***** > Dave Chapman DREA phone: (902) 426-3100 x228 > dave.chapman at drea.dnd.ca FAX: (902) 426-9654 > Symbolic matrix inversion, and symbolic linear algebra in general, tends to suffer from pronounced expression swell. This is a problem we are addressing incrementally; as we improve our simplification capabilities we hope to improve the methods available to symbolic linear algebra as well. Having said all this, the misbehavior you noted was a bug specific to version 2.1 of Mathematica. The linear algebra inversion method switched at 7x7, and for many matrices this was a bad thing. Version 2.2 improved this in two ways, by keeping the default method consistent and by allowing other methods at the user's option. The bug you note in printing is that the formatting code is not easily interruptible. This is a separate problem, and to my knowledge it has not been fixed, at least not in version 2.2. The reason it is not seen in your 6x6 examples is that the method used for those does not (in your matrices) generate such tremendous output, and hence the formatter does not hang on them. Daniel Lichtblau Wolfram Research, Inc.