c  estPi.f
c
c  Program to estimate Pi using random number generation.
c
c  Bruce M. Bolden
c  October 14, 1997
c  -------------------------------------------------------

      program EstPi
c
      integer  nHits
      integer  nTries
      parameter( nTries = 50 )
c
      integer  seed
      real  x, y
c
      nHits = 0
c
      seed = 12357
c     seed = 987653   !  negative values!

      do i = 1, nTries
         call RANDOM(seed, x)
         call RANDOM(seed, y)
         !write(6,*) x
         if( IsInside(x,y) ) then
             nHits = nHits + 1
         endif
      end do
c      
      pi = 4.0 * real(nHits)/real(nTries)
      write( 6, * ) 'Pi: ', pi
c
      stop
      end


c  IsInside
c
c  Test if (x,y) lies inside the unit circle
c
      logical function IsInside( x, y )
      real x, y
c      
      if( x*x + y*y .LE. 1.0 ) then
          IsInside = .TRUE.
      else
          IsInside = .FALSE.
      endif
c
      return
      end


c  RANDOM
c
c  Random number generation subroutine
c
      subroutine RANDOM( iSEED, rand )
      integer iSEED
      real    rand
c      
      iSEED = 2045*iSEED + 1
      iSEED = iSEED - (iSEED/1048576) * 1048576
      rand = real(iSEED+1) / 1048576.0
c
      return
      end