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clacn2.f(3) LAPACK clacn2.f(3)

NAME

clacn2.f

SYNOPSIS

Functions/Subroutines


subroutine clacn2 (N, V, X, EST, KASE, ISAVE)
CLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Function/Subroutine Documentation

subroutine clacn2 (integer N, complex, dimension( * ) V, complex, dimension( * ) X, real EST, integer KASE, integer, dimension( 3 ) ISAVE)

CLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Purpose:


CLACN2 estimates the 1-norm of a square, complex 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 COMPLEX array, dimension (N)
On the final return, V = A*W, where EST = norm(V)/norm(W)
(W is not returned).

X


X is COMPLEX array, dimension (N)
On an intermediate return, X should be overwritten by
A * X, if KASE=1,
A**H * X, if KASE=2,
where A**H is the conjugate transpose of A, and CLACN2 must be
re-called with all the other parameters unchanged.

EST


EST is REAL
On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
unchanged from the previous call to CLACN2.
On exit, EST is an estimate (a lower bound) for norm(A).

KASE


KASE is INTEGER
On the initial call to CLACN2, 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**H * X.
On the final return from CLACN2, 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

Univ. of Colorado Denver

NAG Ltd.

Date:

December 2016

Further Details:


Originally named CONEST, dated March 16, 1988.
Last modified: April, 1999
This is a thread safe version of CLACON, which uses the array ISAVE
in place of a SAVE statement, as follows:
CLACON CLACN2
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 135 of file clacn2.f.

Author

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