DSTERF (3lapack)

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 tridiagonal 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 eigenvalues in a
          total of 30*N iterations; if INFO = i, then i elements of E have
          not converged to zero.