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## zlacon()

subroutine zlacon | ( | integer | n,
|  | complex*16, dimension( n ) | v,
|  | complex*16, dimension( n ) | x,
|  | double precision | est,
|  | integer | kase )

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

Download ZLACON + dependencies [TGZ] [ZIP] [TXT]

Purpose:

      !>
      !> ZLACON estimates the 1-norm of a square, complex matrix A.
      !> Reverse communication is used for evaluating matrix-vector products.
      !>

Parameters

  [in]

  N

      !>          N is INTEGER
      !>         The order of the matrix.  N >= 1.
      !>

  [out]

  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).
      !>

  [in,out]

  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 ZLACON must be
      !>         re-called with all the other parameters unchanged.
      !>

  [in,out]

  EST

      !>          EST is DOUBLE PRECISION
      !>         On entry with KASE = 1 or 2 and JUMP = 3, EST should be
      !>         unchanged from the previous call to ZLACON.
      !>         On exit, EST is an estimate (a lower bound) for norm(A).
      !>

  [in,out]

  KASE

      !>          KASE is INTEGER
      !>         On the initial call to ZLACON, 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 ZLACON, KASE will again be 0.
      !>

Author
  Univ. of Tennessee
  Univ. of California Berkeley
  Univ. of Colorado Denver
  NAG Ltd.

Further Details:
  Originally named CONEST, dated March 16, 1988.
  Last modified: April, 1999

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.