NAME

       dlacon.f -

SYNOPSIS

   Functions/Subroutines
       subroutine dlacon (N, V, X, ISGN, EST, KASE)
           DLACON estimates the 1-norm of a square matrix, using reverse communication for
           evaluating matrix-vector products.

Function/Subroutine Documentation

   subroutine dlacon (integer N, double precision, dimension( * ) V, double precision, dimension(
       * ) X, integer, dimension( * ) ISGN, double precision EST, integer KASE)
       DLACON estimates the 1-norm of a square matrix, using reverse communication for evaluating
       matrix-vector products.

       Purpose:

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

           X

                     X is DOUBLE PRECISION array, dimension (N)
                    On an intermediate return, X should be overwritten by
                          A * X,   if KASE=1,
                          A**T * X,  if KASE=2,
                    and DLACON must be re-called with all the other parameters
                    unchanged.

           ISGN

                     ISGN is INTEGER array, dimension (N)

           EST

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

           KASE

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

       Author:
           Univ. of Tennessee

           Univ. of California Berkeley

           Univ. of Colorado Denver

           NAG Ltd.

       Date:
           September 2012

       Contributors:
           Nick Higham, University of Manchester.
            Originally named SONEST, dated March 16, 1988.

       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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