Hi,
I was wondering how the FEAST algorithm determines the multiplicity of the eigenvalues, for the case of repeated eigenvalues. More precisely, I would like to know if there exists a special tolerance for when two or more eigenvalues are treated as repeated.
The reason behind the questions is that I need the derivative of eigenvalues and thus special treatment is required for the case of repeated eigenvalues, since the eigenvectors of repeated eigenvalue can be linearly combined in an infinite number of ways.
Best,
Anna