SSTERF  - compute all eigenvalues of a symmetric tridiago­
       nal matrix using the Pal-Walker-Kahan variant of the QL or
       QR algorithm


SYNOPSIS

       SUBROUTINE SSTERF( N, D, E, INFO )

           INTEGER        INFO, N

           REAL           D( * ), E( * )


PURPOSE

       SSTERF 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) REAL 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) REAL 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 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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