Purpose

LA_SBGVX and LA_HBGVX compute selected eigenvalues and, optionally, the corresponding eigenvectors of the generalized eigenvalue problem

$$A\,z=\lambda\,B\,z,$$

where $A$ and $B$ are real symmetric in the case of LA_SBGVX and complex Hermitian in the case of LA_HBGVX. In both cases $B$ is positive definite. Matrices $A$ and $B$ are stored in a band format. Eigenvalues and eigenvectors can be selected by specifying either a range of values or a range of indices for the desired eigenvalues.