clacn2.f(3)

NAME
clacn2.f

SYNOPSIS

  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.

Function/Subroutine Documentation

  subroutine clacn2 (integer N, complex, dimension( * ) V, complex, dimension( * ) X, real EST, integer KASE, integer, dimension( 3 ) ISAVE)

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.

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 132 of file clacn2.f.

Author

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