The Lanczos algorithm for the symmetric Ax = $\lambda$Bx problem.

The problem of computing the eigensystem of Ax = $\lambda$Bx when A and B are symmetric and B is positive definite is considered. A generalization of the Lanczos algorithm for reducing the problem to a symmetric tridiagonal eigenproblem is given. A numerically stable variant of the algorithm is described. The new algorithm depends heavily upon the computation of elementary Hermitian matrices. An ALGOL W procedure and a numerical example are also given.