DLACON(l) ) DLACON(l)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 commu‐
nication is used for evaluating matrix-vector products.
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 interme‐
diate return, KASE will be 1 or 2, indicating whether X should
be overwritten by A * X or A' * X. On the final 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 condition estimation", ACM
Trans. Math. Soft., vol. 14, no. 4, pp. 381-396, December 1988.
LAPACK version 3.0 15 June 2000 DLACON(l)
