clacn2.f File Reference

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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.

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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.

Download CLACN2 + dependencies [TGZ] [ZIP] [TXT]

Purpose:

 CLACN2 estimates the 1-norm of a square, complex matrix A.
 Reverse communication is used for evaluating matrix-vector products.

Parameters:

[in]	N	N is INTEGER The order of the matrix. N >= 1.
[out]	V	V is COMPLEX array, dimension (N) On the final return, V = A*W, where EST = norm(V)/norm(W) (W is not returned).
[in,out]	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.
[in,out]	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).
[in,out]	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.
[in,out]	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.

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