slacn2.f (3)

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.

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

Univ. of Colorado Denver

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.

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