slacn2.f (3) - Linux Man Pages

slacn2.f -

SYNOPSIS

Functions/Subroutines

subroutine slacn2 (N, V, X, ISGN, EST, KASE, ISAVE)
SLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Function/Subroutine Documentation

subroutine slacn2 (integerN, real, dimension( * )V, real, dimension( * )X, integer, dimension( * )ISGN, realEST, integerKASE, integer, dimension( 3 )ISAVE)

SLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Purpose:

SLACN2 estimates the 1-norm of a square, real matrix A.
Reverse communication is used for evaluating matrix-vector products.

Parameters:

N

N is INTEGER
The order of the matrix.  N >= 1.

V

V is REAL array, dimension (N)
On the final return, V = A*W,  where  EST = norm(V)/norm(W)
(W is not returned).

X

X is REAL array, dimension (N)
On an intermediate return, X should be overwritten by
A * X,   if KASE=1,
A**T * X,  if KASE=2,
and SLACN2 must be re-called with all the other parameters
unchanged.

ISGN

ISGN is INTEGER array, dimension (N)

EST

EST is REAL
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to SLACN2.
On exit, EST is an estimate (a lower bound) for norm(A).

KASE

KASE is INTEGER
On the initial call to SLACN2, 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**T * X.
On the final return from SLACN2, KASE will again be 0.

ISAVE

ISAVE is INTEGER array, dimension (3)
ISAVE is used to save variables between calls to SLACN2

Author:

Univ. of Tennessee

Univ. of California Berkeley

NAG Ltd.

Date:

September 2012

Further Details:

Originally named SONEST, dated March 16, 1988.

This is a thread safe version of SLACON, which uses the array ISAVE
in place of a SAVE statement, as follows:

SLACON     SLACN2
JUMP     ISAVE(1)
J        ISAVE(2)
ITER     ISAVE(3)

Contributors:

Nick Higham, University of Manchester

References:

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.

Definition at line 137 of file slacn2.f.

Author

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