Purpose

LA_SBEV and LA_SBEVD compute all eigenvalues and, optionally, all eigenvectors of a real symmetric matrix $A$ in band form.
LA_HBEV and LA_HBEVD compute all eigenvalues and, optionally, all eigenvectors of a complex Hermitian matrix $A$ in band form.
LA_SBEVD and LA_HBEVD use a divide and conquer algorithm. They are much faster than LA_SBEV and LA_HBEV for large matrices but use more workspace.