Name

ran69069 − Routine to generate single precision random numbers using a=69069 and m=2∗∗32

FORMAT

RAN69069 (s)

Function Value

ran69069real∗4
The uniform[0,1] value returned.

Arguments

sinteger∗4
On input, a seed s being set initially or left unchanged from a previous iteration. 
On exit, the updated seed.

Description

The RAN69069 routine computes updated seeds using the linear multiplicative algorithm as follows:

s = 69069∗s+1, mod 2∗∗32

and returns s∗2.0∗∗(-32), as its uniform [0,1] output. 

The following code example simulates a random walk using RAN69069. A particle starts at (0,0) and proceeds N., E., S., or W. with probability 0.25 each. 

Example

      integer ix,iy,i,j,iseed,nsteps,nwalks
      real∗4 x
c     random walk: go N E S W each with probability 0.25
      nsteps = 1000000
      nwalks = 10
      iseed = 1234
       do j=1,nwalks
      ix=0
      iy=0
      do i = 1, nsteps
      x=ran69069(iseed)
      if(x.le.0.25)then
         ix=ix+1
      else if(x.le.0.5)then
         iy=iy+1
      else if(x.le.0.75)then
         ix=ix-1
      else
         iy=iy-1
      end if
      end do
       print∗,’final position ’,ix,iy
      end do
      end