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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