MA01BZ

Safely computing the general product of K complex scalars

Purpose

  To compute the general product of K complex scalars trying to
  avoid over- and underflow.

      SUBROUTINE MA01BZ( BASE, K, S, A, INCA, ALPHA, BETA, SCAL )
C     .. Scalar Arguments ..
      INTEGER           INCA, K, SCAL
      DOUBLE PRECISION  BASE
      COMPLEX*16        ALPHA, BETA
C     .. Array Arguments ..
      INTEGER           S(*)
      COMPLEX*16        A(*)

Input/Output Parameters

  BASE    (input)  DOUBLE PRECISION
          Machine base.

  K       (input)  INTEGER
          The number of scalars.  K >= 1.

  S       (input)  INTEGER array, dimension (K)
          The signature array. Each entry of S must be 1 or -1.

  A       (input)  COMPLEX*16 array, dimension (K)
          Vector of complex scalars.

  INCA    (input)  INTEGER
          Increment for the array A. INCA <> 0.

  ALPHA   (output)  COMPLEX*16
          ALPHA is a complex scalar with ABS(ALPHA) = 0, or
          1.0 <= ABS(ALPHA) < BASE, such that

             ALPHA / BETA * BASE**(SCAL)

          is the general product of the scalars in the array A.

  BETA    (output)  COMPLEX*16
          BETA is either 0.0 or 1.0.
          See also the description of ALPHA.

  SCAL    (output)  INTEGER
          Scaling factor exponent, see ALPHA.

  None

Program Text

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