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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( * )



     #include <sunperf.h>

     void dlacon(int n, double *v, double *dx, int *isgn,  double
               *est, int *kase) ;

PURPOSE
     DLACON estimates the 1-norm of  a  square,  real  matrix  A.
     Reverse  communication  is used for evaluating matrix-vector
     products.  If the initial call is made with  KASE  equal  to
     -255  and  subsequent  intermediate  calls made as described
     below then this subroutine is MT-safe, otherwise it  is  not
     MT-safe.

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 MT-unsafe 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.  On an MT-safe intermediate
               return, X should be overwritten by A * X  if  bits
               8-11  of  KASE=0001,  A'  *  X  if  bits  8-11  of
               KASE=0010, and DLACON must be re-called  with  all
               the  other parameters unchanged.  The MT-safe mode
               is described below in the description of the  KASE
               argument.

     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 or
               -255.   If  KASE  was supplied as 0 on the initial
               call then on an intermediate return, KASE will  be
               1 or 2, indicating whether X should be overwritten
               by A * X  or A' * X.  If KASE was supplied as -255
               on  the  initial  call  then  on  an  intermediate
               return, the low 8 bits of KASE will be 0  and  the
               next  4  bits  will  contain  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.  If the initial call is made with KASE
               equal  to -255 then this subroutine is MT-safe but
               does not conform to the  standard  LAPACK  calling
               sequence.   If  the initial call is made with KASE
               equal to 0 then it is not MT-safe, but it conforms
               to the standard LAPACK calling sequence.

FURTHER DETAILS
     Contributed by Nick Higham, University of Manchester.
     Originally named SONEST, dated 27 Jun 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.

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