dlacn2.f(3)

NAME
dlacn2.f -

SYNOPSIS

  Functions/Subroutines
subroutine dlacn2 (N, V, X, ISGN, EST, KASE, ISAVE)
DLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Function/Subroutine Documentation

  subroutine dlacn2 (integerN, double precision, dimension( * )V, double precision, dimension( * )X, integer, dimension( * )ISGN, double precisionEST, integerKASE, integer, dimension( 3 )ISAVE)

DLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Purpose:

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

Parameters:
    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

Author:
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Date:
    September 2012

Further Details:

      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)

Contributors:
    Nick Higham, University of Manchester

References:
    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.

Definition at line 137 of file dlacn2.f.

Author

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