clacn2.f man page

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.

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.