From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 107079,c7637cfdf68e766 X-Google-Attributes: gid107079,public X-Google-Thread: 109d8a,c7637cfdf68e766 X-Google-Attributes: gid109d8a,public X-Google-Thread: f8362,c7637cfdf68e766 X-Google-Attributes: gidf8362,public X-Google-Thread: f43e6,c7637cfdf68e766 X-Google-Attributes: gidf43e6,public X-Google-Thread: 103376,c7637cfdf68e766 X-Google-Attributes: gid103376,public From: fyodor@sally.nas.nasa.gov (Chris L. Kuszmaul) Subject: Re: floating point comparison Date: 1997/09/03 Message-ID: <5uknb2$cnp$1@cnn.nas.nasa.gov>#1/1 X-Deja-AN: 269778689 Distribution: inet References: <5ud3mc$5d2$1@news.fsu.edu> Organization: NAS - NASA Ames Research Center, Moffett Field, CA Newsgroups: comp.lang.ada,sci.math.num-analysis,comp.software-eng,comp.theory,sci.math Date: 1997-09-03T00:00:00+00:00 List-Id: In article checker@netcom.com (Chris Hecker) writes: > >I don't mean to flame here, because I agree that precise terminology is >very important, but do you guys (or anyone) actually have any useful >and applicable hints for someone trying to make numerical code work? If you are doing matrix operations, then you can get good error estimates from commercial packages without doing much work. If your error margins are large, then you may need to find out the condition number of your matrix (or matrices), and see if you can reduce this. It may turn out that the nature of the problem you are trying to solve is fundamentally prone to error. > >Completely analyzing a quadratic equation makes for a great Chapter 1 >(as does a mention of the e^-x series and the other classics), but I've >got the results of a quadratic solve determining some elements of >vectors that get fed through a gaussian eliminator and they're supposed >to be compatible systems but the input data is slightly off and...you >get the point. > I would begin with the matrix you generate with your quadratic solve. I would get a hold of a commercial linear system solver package and find out the estimated condition number of the matrix you are going Gaussian elimination on. If this shows a near-singular matrix, then one problem is in the creation of the matrix (or something fundamental about your problem). If the matrix is well conditioned, then you need to look more closely at errors introduced in the 'quadratic solve'. CLK