# SRC/dlacon.c File Reference

Estimates the 1-norm. More...

`#include <math.h>`
`#include "slu_Cnames.h"`

## Defines
#define | d_sign(a, b) (b >= 0 ? fabs(a) : -fabs(a))
#define | i_dnnt(a) ( a>=0 ? floor(a+.5) : -floor(.5-a) )
## Functions
int | dlacon_ (int *n, double *v, double *x, int *isgn, double *est, int *kase)

## Detailed Description

     -- SuperLU routine (version 2.0) --
     Univ. of California Berkeley, Xerox Palo Alto Research Center,
     and Lawrence Berkeley National Lab.
     November 15, 1997

## Define Documentation

#define d_sign | ( | a,
|  | b |  | ) | (b >= 0 ? fabs(a) : -fabs(a))

#define i_dnnt | ( | a |  | ) | ( a>=0 ? floor(a+.5) : -floor(.5-a) )

## Function Documentation

int dlacon_ | ( | int * | n,
|  | double * | v,
|  | double * | x,
|  | int * | isgn,
|  | double * | est,
|  | int * | kase |
| ) |  |  |

       Purpose
       =======

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

       Arguments
       =========

       N      (input) INT
              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) INT array, dimension (N)

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

       KASE   (input/output) INT
              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 CONEST, 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.
       =====================================================================