NAME

       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.

       Date:
           September 2012

       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.

Author

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