DLACN2(3)      LAPACK routine of NEC Numeric Library Collection      DLACN2(3)



NAME
       DLACN2

SYNOPSIS
       SUBROUTINE DLACN2 (N, V, X, ISGN, EST, KASE, ISAVE)



PURPOSE
            DLACN2 estimates the 1-norm of a square, real matrix A.
            Reverse communication is used for evaluating matrix-vector products.




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

           V         (output)
                     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         (input/output)
                     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 DLACN2 must be re-called with all the other parameters
                    unchanged.

           ISGN      (output)
                     ISGN is INTEGER array, dimension (N)

           EST       (input/output)
                     EST is DOUBLE PRECISION
                    On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
                    unchanged from the previous call to DLACN2.
                    On exit, EST is an estimate (a lower bound) for norm(A).

           KASE      (input/output)
                     KASE is INTEGER
                    On the initial call to DLACN2, 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 DLACN2, KASE will again be 0.

           ISAVE     (input/output)
                     ISAVE is INTEGER array, dimension (3)
                    ISAVE is used to save variables between calls to DLACN2






FURTHER DETAILS
             This is a thread safe version of DLACON, which uses the array ISAVE
             in place of a SAVE statement, as follows:

                DLACON     DLACN2
                 JUMP     ISAVE(1)
                 J        ISAVE(2)
                 ITER     ISAVE(3)



LAPACK routine                  31 October 2017                      DLACN2(3)