pb_drand()

double precision function pb_drand

(

integer

idumm

)

Definition at line 2119 of file pdblastim.f.

*
*  -- PBLAS test routine (version 2.0) --
*     University of Tennessee, Knoxville, Oak Ridge National Laboratory,
*     and University of California, Berkeley.
*     April 1, 1998
*
*     .. Scalar Arguments ..
      INTEGER            IDUMM
*     ..
*
*  Purpose
*  =======
*
*  PB_DRAND generates the next number in the random sequence. This func-
*  tion ensures that this number will be in the interval ( -1.0, 1.0 ).
*
*  Arguments
*  =========
*
*  IDUMM   (local input) INTEGER
*          This argument is ignored, but necessary to a FORTRAN 77 func-
*          tion.
*
*  Further Details
*  ===============
*
*  On entry, the array IRAND stored in the common block  RANCOM contains
*  the information (2 integers)  required to generate the next number in
*  the sequence X( n ). This number is computed as
*
*     X( n ) = ( 2^16 * IRAND( 2 ) + IRAND( 1 ) ) / d,
*
*  where the constant d is the  largest  32 bit  positive  integer.  The
*  array  IRAND  is  then  updated for the generation of the next number
*  X( n+1 ) in the random sequence as follows X( n+1 ) = a * X( n ) + c.
*  The constants  a  and c  should have been preliminarily stored in the
*  array  IACS  as  2 pairs of integers. The initial set up of IRAND and
*  IACS is performed by the routine PB_SETRAN.
*
*  -- Written on April 1, 1998 by
*     Antoine Petitet, University  of  Tennessee, Knoxville 37996, USA.
*
*  =====================================================================
*
*     .. Parameters ..
      DOUBLE PRECISION   ONE, TWO
      parameter( one = 1.0d+0, two = 2.0d+0 )
*     ..
*     .. External Functions ..
      DOUBLE PRECISION   PB_DRAN
      EXTERNAL           pb_dran
*     ..
*     .. Executable Statements ..
*
      pb_drand = one - two * pb_dran( idumm )
*
      RETURN
*
*     End of PB_DRAND
*

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