dlacon(3F)

NAME
     DLACON - estimate the 1-norm of a square, real matrix A

SYNOPSIS
     SUBROUTINE DLACON( N, V, X, ISGN, EST, KASE )

         INTEGER        KASE, N

         DOUBLE         PRECISION EST

         INTEGER        ISGN( * )

         DOUBLE         PRECISION V( * ), X( * )

PURPOSE
     DLACON estimates the 1-norm of a square, real matrix A.  Reverse
     communication is used for evaluating matrix-vector products.


ARGUMENTS
     N      (input) INTEGER
            The order of the matrix.  N >= 1.

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

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

     ISGN   (workspace) INTEGER array, dimension (N)

     EST    (output) DOUBLE PRECISION
            An estimate (a lower bound) for norm(A).

     KASE   (input/output) 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' * X.  On the final return
            from DLACON, KASE will again be 0.

FURTHER DETAILS
     Contributed by Nick Higham, University of Manchester.
     Originally named SONEST, dated March 16, 1988.

     Reference: 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.