ZLACN2 estimates the 1-norm of a square, complex 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 COMPLEX*16 array, dimension (N)


         On the final return, V = A*W,  where  EST = norm(V)/norm(W)


         (W is not returned).

X

          X is COMPLEX*16 array, dimension (N)


         On an intermediate return, X should be overwritten by


               A * X,   if KASE=1,


               A**H * X,  if KASE=2,


         where A**H is the conjugate transpose of A, and ZLACN2 must be


         re-called with all the other parameters unchanged.

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 ZLACN2.


         On exit, EST is an estimate (a lower bound) for norm(A).

KASE

          KASE is INTEGER


         On the initial call to ZLACN2, 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**H * X.


         On the final return from ZLACN2, KASE will again be 0.

ISAVE

          ISAVE is INTEGER array, dimension (3)


         ISAVE is used to save variables between calls to ZLACN2

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

December 2016

  Originally named CONEST, dated March 16, 1988.


  Last modified:  April, 1999


  This is a thread safe version of ZLACON, which uses the array ISAVE


  in place of a SAVE statement, as follows:


     ZLACON     ZLACN2


      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.