NAME

       sterf - sterf: eig, QR iteration

SYNOPSIS

   Functions
       subroutine dsterf (n, d, e, info)
           DSTERF
       subroutine ssterf (n, d, e, info)
           SSTERF

Detailed Description

Function Documentation

   subroutine dsterf (integer n, double precision, dimension( * ) d, double precision, dimension(
       * ) e, integer info)
       DSTERF

       Purpose:

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

       Parameters
           N

                     N is INTEGER
                     The order of the matrix.  N >= 0.

           D

                     D is 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

                     E is DOUBLE PRECISION array, dimension (N-1)
                     On entry, the (n-1) subdiagonal elements of the tridiagonal
                     matrix.
                     On exit, E has been destroyed.

           INFO

                     INFO is 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.

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

   subroutine ssterf (integer n, real, dimension( * ) d, real, dimension( * ) e, integer info)
       SSTERF

       Purpose:

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

       Parameters
           N

                     N is INTEGER
                     The order of the matrix.  N >= 0.

           D

                     D is REAL array, dimension (N)
                     On entry, the n diagonal elements of the tridiagonal matrix.
                     On exit, if INFO = 0, the eigenvalues in ascending order.

           E

                     E is REAL array, dimension (N-1)
                     On entry, the (n-1) subdiagonal elements of the tridiagonal
                     matrix.
                     On exit, E has been destroyed.

           INFO

                     INFO is 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.

       Author
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

Author

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