Re: [Lapackpp-devel] LaLinearSolve not totally exact

[Christian S. <sti...@tu...>]

Am Dienstag, 10. August 2004 21:38 schrieb Jacob \(Jack\) Gryn:
> I tried it out again with both square and non-square matricies on both
> complex and doubles:
>
> Results are the same for both Complex matricies and Doubles.
>
> With square matrices, the results are more viable.  The equation AX=B, with
> A and B being the same, X should return the identity matrix; however it
> does not.  Although through multiplying AX, the result still is B.
>
> With rectangular matrices, the results are the same in both complex and
> doubles, but AX != B;  X is usually all 0's, or very close to 0's
> (10e-300).

When you say AX != B, how large is the actual difference, that is D=(AX-B) and 
what is the Mat_Norm2(D)? If that's in fact in the region of 10e-15 or 
smaller, then you are only seeing some rounding effects due to the floating 
point representation -- I wouldn't consider this a problem. If you have 
matrices with numbers in normal regions, then simply consider anything below 
10^-10 as zero and you're fine. Did I misunderstand something?

Christian