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Fortran Programming Language
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Arpack usage
Hello,
I am now involved in using arpack to solve a large complex matrix's
eigenvalues and corresponding eigenvectors. The solver I used is
arpack, it's really great, fast and convenient.
I compare the eigenvalues and eigenvectors from arpack solver and
matlab 'eigs' function (though I know it also uses arpack), however, I
found a big mismatch on eigenvectors (eigenvalue is OK, they match!)
Can anyone who have used arpack tell me why such big mismatch exist?
Thanks a lot,
lorin
On May 14, 9:29 am, lorin <wwang@gmail.com> wrote:
> Hello, > I am now involved in using arpack to solve a large complex matrix's
> eigenvalues and corresponding eigenvectors. The solver I used is
> arpack, it's really great, fast and convenient.
> I compare the eigenvalues and eigenvectors from arpack solver and
> matlab 'eigs' function (though I know it also uses arpack), however, I
> found a big mismatch on eigenvectors (eigenvalue is OK, they match!)
> Can anyone who have used arpack tell me why such big mismatch exist?
Matlab may use different conventions in scaling the eigenvectors. Are
the arpack eigenvectors proportional to those of Matlab?
On 14 mei, 15:29, lorin <wwang@gmail.com> wrote:
> Hello, > I am now involved in using arpack to solve a large complex matrix's
> eigenvalues and corresponding eigenvectors. The solver I used is
> arpack, it's really great, fast and convenient.
> I compare the eigenvalues and eigenvectors from arpack solver and
> matlab 'eigs' function (though I know it also uses arpack), however, I
> found a big mismatch on eigenvectors (eigenvalue is OK, they match!)
> Can anyone who have used arpack tell me why such big mismatch exist?
> Thanks a lot,
> lorin
get any
linear combination of the eigenvectors. That is one possible
explanation.
Another is: have you normalised the vectors before comparing them?
There
could be a (complex) factor between them.
Regards,
Arjen
On May 14, 9:42 pm, Arjen Markus <arjen.mar@wldelft.nl> wrote:
> On 14 mei, 15:29, lorin <wwang @gmail.com> wrote: > > Hello,
> > I am now involved in using arpack to solve a large complex matrix's
> > eigenvalues and corresponding eigenvectors. The solver I used is
> > arpack, it's really great, fast and convenient.
> > I compare the eigenvalues and eigenvectors from arpack solver and
> > matlab 'eigs' function (though I know it also uses arpack), however, I
> > found a big mismatch on eigenvectors (eigenvalue is OK, they match!)
> > Can anyone who have used arpack tell me why such big mismatch exist?
> > Thanks a lot,
> > lorin
> Perhaps you have eigenvalues that (nearly) coincide? Then you could
> get any
> linear combination of the eigenvectors. That is one possible
> explanation.
> Another is: have you normalised the vectors before comparing them?
> There
> could be a (complex) factor between them.
> Regards,
> Arjen
Matlab and ARPACK. There is a factor between them, for different
matrix, the factor is not the same, but all factors' absolute
magnitude is unit length. I try to find out why such factor exists,
but it seems difficult...
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