slacon(3)

NAME

SLACON - estimate the 1-norm of a square, real matrix A

SYNOPSIS

SUBROUTINE SLACON( N, V, X, ISGN, EST, KASE )
    INTEGER        KASE, N
    REAL           EST
    INTEGER        ISGN( * )
    REAL           V( * ), X( * )

PURPOSE

SLACON estimates the 1-norm of a square, real matrix A.

Reverse communication is used for evaluating matrix-vector prod

ucts.

ARGUMENTS

N (input) INTEGER

The order of the matrix. N >= 1.

V (workspace) REAL array, dimension (N)

On the final return, V = A*W, where EST =

norm(V)/norm(W) (W is not returned).

X (input/output) REAL array, dimension (N)

On an intermediate return, X should be overwritten

by A * X, if KASE=1, A' * X, if KASE=2, and SLACON must be re

called with all the other parameters unchanged.

ISGN (workspace) INTEGER array, dimension (N)

EST (output) REAL

An estimate (a lower bound) for norm(A).

KASE (input/output) INTEGER

On the initial call to SLACON, KASE should be 0.

On an intermediate return, KASE will be 1 or 2, indicating

whether X should be overwritten by A * X or A' * X. On the fi

nal return from SLACON, KASE will again be 0.

FURTHER DETAILS

Contributed by Nick Higham, University of Manchester.
Originally named SONEST, dated March 16, 1988.

Reference: N.J. Higham, "FORTRAN codes for estimating the

one-norm of a real or complex matrix, with applications to condi

tion estimation", ACM Trans. Math. Soft., vol. 14, no. 4, pp.

381-396, December 1988.

LAPACK version 3.0 15 June 2000

SLACON(3)