SRC/slacn2.f(3)

NAME
SRC/slacn2.f

SYNOPSIS

  Functions/Subroutines
subroutine slacn2 (n, v, x, isgn, est, kase, isave)
SLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Function/Subroutine Documentation

  subroutine slacn2 (integer n, real, dimension( * ) v, real, dimension( * ) x, integer, dimension( * ) isgn, real est, integer kase, integer, dimension( 3 ) isave)

SLACN2 estimates the 1-norm of a square matrix, using reverse communication for evaluating matrix-vector products.

Purpose:

     SLACN2 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 REAL array, dimension (N)
             On the final return, V = A*W,  where  EST = norm(V)/norm(W)
             (W is not returned).

    X

              X is REAL array, dimension (N)
             On an intermediate return, X should be overwritten by
                   A * X,   if KASE=1,
                   A**T * X,  if KASE=2,
             and SLACN2 must be re-called with all the other parameters
             unchanged.

    ISGN

              ISGN is INTEGER array, dimension (N)

    EST

              EST is REAL
             On entry with KASE = 1 or 2 and ISAVE(1) = 3, EST should be
             unchanged from the previous call to SLACN2.
             On exit, EST is an estimate (a lower bound) for norm(A).

    KASE

              KASE is INTEGER
             On the initial call to SLACN2, 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 SLACN2, KASE will again be 0.

    ISAVE

              ISAVE is INTEGER array, dimension (3)
             ISAVE is used to save variables between calls to SLACN2

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Further Details:

      Originally named SONEST, dated March 16, 1988.
      This is a thread safe version of SLACON, which uses the array ISAVE
      in place of a SAVE statement, as follows:
         SLACON     SLACN2
          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 135 of file slacn2.f.

Author

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