slacn2()

subroutine slacn2	(	integer	n,
		real, dimension( * )	v,
		real, dimension( * )	x,
		integer, dimension( * )	isgn,
		real	est,
		integer	kase,
		integer, dimension( 3 )	isave )

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

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Purpose:

!>
!> SLACN2 estimates the 1-norm of a square, real 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 REAL 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 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. !>
[out]	ISGN	!> ISGN is INTEGER array, dimension (N) !>
[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 SLACN2. !> On exit, EST is an estimate (a lower bound) for norm(A). !>
[in,out]	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. !>
[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.

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.