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 DLA­
              CON 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,



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