SRC/zlacn2.f(3)

NAME
SRC/zlacn2.f

SYNOPSIS

  Functions/Subroutines
subroutine zlacn2 (n, v, x, est, kase, isave)
ZLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Function/Subroutine Documentation

  subroutine zlacn2 (integer n, complex*16, dimension( * ) v, complex*16, dimension( * ) x, double precision est, integer kase, integer, dimension( 3 ) isave)

ZLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Purpose:

     ZLACN2 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*16 array, dimension (N)
             On the final return, V = A*W,  where  EST = norm(V)/norm(W)
             (W is not returned).

    X

              X is COMPLEX*16 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 ZLACN2 must be
             re-called with all the other parameters unchanged.

    EST

              EST is DOUBLE PRECISION
             On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
             unchanged from the previous call to ZLACN2.
             On exit, EST is an estimate (a lower bound) for norm(A).

    KASE

              KASE is INTEGER
             On the initial call to ZLACN2, 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 ZLACN2, KASE will again be 0.

    ISAVE

              ISAVE is INTEGER array, dimension (3)
             ISAVE is used to save variables between calls to ZLACN2

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

      Originally named CONEST, dated March 16, 1988.
      Last modified:  April, 1999
      This is a thread safe version of ZLACON, which uses the array ISAVE
      in place of a SAVE statement, as follows:
         ZLACON     ZLACN2
          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 132 of file zlacn2.f.

Author

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