dlacon(3)

NAME

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

SYNOPSIS

SUBROUTINE DLACON( N, V, X, ISGN, EST, KASE )
    INTEGER        KASE, N
    DOUBLE         PRECISION EST
    INTEGER        ISGN( * )
    DOUBLE         PRECISION V( * ), X( * )

PURPOSE

DLACON 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) DOUBLE PRECISION array, dimension (N)

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

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

X (input/output) DOUBLE PRECISION array, dimension

(N)

On an intermediate return, X should be overwritten

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

called with all the other parameters unchanged.

ISGN (workspace) INTEGER array, dimension (N)

EST (output) DOUBLE PRECISION

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

KASE (input/output) INTEGER

On the initial call to DLACON, 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 DLACON, 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

DLACON(3)