.TH DLACN2 1 "November 2006" " LAPACK auxiliary routine (version 3.1) " " LAPACK auxiliary routine (version 3.1) "
.SH NAME
DLACN2 - the 1-norm of a square, real matrix A
.SH SYNOPSIS
.TP 19
SUBROUTINE DLACN2(
N, V, X, ISGN, EST, KASE, ISAVE )
.TP 19
.ti +4
INTEGER
KASE, N
.TP 19
.ti +4
DOUBLE
PRECISION EST
.TP 19
.ti +4
INTEGER
ISGN( * ), ISAVE( 3 )
.TP 19
.ti +4
DOUBLE
PRECISION V( * ), X( * )
.SH PURPOSE
DLACN2 estimates the 1-norm of a square, real matrix A.
Reverse communication is used for evaluating matrix-vector products.
.SH ARGUMENTS
.TP 7
N (input) INTEGER
The order of the matrix. N >= 1.
.TP 7
V (workspace) DOUBLE PRECISION array, dimension (N)
On the final return, V = A*W, where EST = norm(V)/norm(W)
(W is not returned).
.TP 7
X (input/output) DOUBLE PRECISION array, dimension (N)
On an intermediate return, X should be overwritten by
A * X, if KASE=1,
A\(aq * X, if KASE=2,
and DLACN2 must be re-called with all the other parameters
unchanged.
.TP 7
ISGN (workspace) INTEGER array, dimension (N)
.TP 7
EST (input/output) DOUBLE PRECISION
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to DLACN2.
On exit, EST is an estimate (a lower bound) for norm(A).
.TP 7
KASE (input/output) INTEGER
On the initial call to DLACN2, 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\(aq * X.
On the final return from DLACN2, KASE will again be 0.
.TP 7
ISAVE (input/output) INTEGER array, dimension (3)
ISAVE is used to save variables between calls to DLACN2
.SH FURTHER DETAILS
Contributed by Nick Higham, University of Manchester.
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Originally named SONEST, dated March 16, 1988.
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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.
This is a thread safe version of DLACON, which uses the array ISAVE
in place of a SAVE statement, as follows:
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DLACON DLACN2
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JUMP ISAVE(1)
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J ISAVE(2)
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ITER ISAVE(3)
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