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dsterf

 NAME
      DSTERF - compute all eigenvalues of a symmetric tridiagonal
      matrix using the Pal-Walker-Kahan variant of the QL or QR
      algorithm

 SYNOPSIS
      SUBROUTINE DSTERF( N, D, E, INFO )

          INTEGER        INFO, N

          DOUBLE         PRECISION D( * ), E( * )

 PURPOSE
      DSTERF computes all eigenvalues of a symmetric tridiagonal
      matrix using the Pal-Walker-Kahan variant of the QL or QR
      algorithm.

 ARGUMENTS
      N       (input) INTEGER
              The order of the matrix.  N >= 0.

      D       (input/output) DOUBLE PRECISION array, dimension (N)
              On entry, the n diagonal elements of the tridiagonal
              matrix.  On exit, if INFO = 0, the eigenvalues in
              ascending order.

      E       (input/output) DOUBLE PRECISION array, dimension (N-
              1)
              On entry, the (n-1) subdiagonal elements of the tri-
              diagonal matrix.  On exit, E has been destroyed.

      INFO    (output) INTEGER
              = 0:  successful exit
              < 0:  if INFO = -i, the i-th argument had an illegal
              value
              > 0:  the algorithm failed to find all of the eigen-
              values in a total of 30*N iterations; if INFO = i,
              then i elements of E have not converged to zero.