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LAPACK version 3.0
dsterf(3)

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

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

      INTEGER	     INFO, N

      DOUBLE	     PRECISION D( * ), E( * )

DESCRIPTION
  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.