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EA22 Sparse symmetric: simultaneous iteration

Given a real symmetric matrix A = {aij}n×n of order n, calculates the k largest eigenvalues, λ1 λ2 ,..., λk and their associated eigenvectors xi,i = 1,2,...,k, where Axi = λixi. The subroutine uses the method of simultaneous iteration and also allows the user to take advantage of sparsity. Eigensolutions from other parts of the spectrum can be obtained by using shifts of the form A βI optionally combined with inversion.