eigenvalues with smallest real part in eigs

Hi,

I need to find the first "n" eigenvalues "a" of smallest real part and its corresponding eigenvectors of the following eigenvalue problem

A*v = a*B*v

with A non-singular and non-symmetric, and B symmetric and positive definite, and the eigenvalues must be always have postiive real part (A and B comes from a mechanical system). I tried with

[v,a]=eigs(A,B,n,'SR')

and

opts.cholB=1;
[v,a]=eigs(A,chol(B),n,'SR',opts);

but the algorithm cannot converge in both cases. However, in the case of using 'LR' and it seems to work fine.

Does anybody know the reason?

Do you know if it is possible to use the option 'SR' in the case that B is only postive semi-definite?

Thanks in advance,

Cristobal.
.

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