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Re: Good eigenvalue/eigenvector test problems for eigs?
From: |
David Bateman |
Subject: |
Re: Good eigenvalue/eigenvector test problems for eigs? |
Date: |
Sat, 23 Sep 2006 08:08:00 +0200 |
User-agent: |
Thunderbird 1.5.0.5 (X11/20060817) |
Sebastien Loisel wrote:
> This was my thinking as well, the the problem should be easy. By try the
> code I supplied under matlab and see what you get for "det(A - lamba *
> eye(n))".
>
>
> for k=1:n foo(k)=det(B-ei(k)*eye(n)); end;
> plot(foo);
>
> for the complex matrices shows that the det is <= 10^-20.
>
> Sébastien Loisel
>
Ok, I have to kill my sysadmin... It seems he only partially fixed the
-ffloat-store problem with atlas on my machine, as octave works fine for
the first matrix if I disable atlas... Could someone on fedora or debian
check
n=200;
A = spdiags([ones(n,1),4*ones(n,1),-ones(n,1)],[-2,0,2],n,n);
d0=eig(A);
merr=0.
for i=1:200
newerr = abs(det(A - d0(i)*eye(n)));
if (newerr > merr)
merr = newerr;
endif
endfor
printf("Max error: %g\n", merr);
and see that you get an error around 1e-20 and not 1e+200 like I do with
my atlas. I'd like to know if this atlas issue exists elsewhere, and if
not point my sysadmin to a distrib that has the right fix..
D>
Re: Good eigenvalue/eigenvector test problems for eigs?, Sebastien Loisel, 2006/09/22