DLACN2 estimates the 1-norm of a square, real matrix A.


 Reverse communication is used for evaluating matrix-vector products.

N

          N is INTEGER


         The order of the matrix.  N >= 1.

V

          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

          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

          ISGN is INTEGER array, dimension (N)

EST

          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

          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

          ISAVE is INTEGER array, dimension (3)


         ISAVE is used to save variables between calls to DLACN2

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

September 2012

  Originally named SONEST, dated March 16, 1988.


  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)

Nick Higham, University of Manchester

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.