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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( * )



     #include <sunperf.h>

     void dsterf(int n, double *d, double *e, int *info) ;

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 tridiago-
               nal 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 des-
               troyed.

     INFO      (output) INTEGER
               = 0:  successful exit
               < 0:  if INFO = -i, the i-th argument had an ille-
               gal 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.

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