The documentation writes:
eigs(A,k,sigma), where A is the sparse matrix, k is the number of eigenvalues and sigma can be scalar or discriptive flag like 'sm'.
However, is it possible to both set the sigma shift andthe direction of eigenvalue?
For example, I want to find the largest real eigenvalue after shift sigma, it seems that I need to both assign sigma to be the value of shift(like (A-sigma*I)^-1 in ARPACK) and sigma to be 'lr'. But how to acheive this since I can only give one sigma value?
The reason that I want to acheive this is because I want to find the eigenvalue that is closest to sigma but also larger than sigma.
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