Block Lanczos algorithm

The Block Lanczos algorithm is a numerical method used for approximating eigenvalues and eigenvectors of large symmetric (or Hermitian) matrices. It is an extension of the classical Lanczos algorithm, which is designed for finding eigenvalues of large sparse matrices efficiently. The block version can handle multiple eigenvalues and eigenvectors simultaneously, making it particularly useful in scenarios where one needs to compute several eigenpairs at once.