clacn2-f(3)

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 (integerN, complex, dimension( * )V, complex, dimension( * )X, realEST, integerKASE, 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 is INTEGER
 The order of the matrix. N >= 1.

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

 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:

September 2012

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 134 of file clacn2.f.

Author

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