c ======================================================================
c     usage: partdemo0 <np>
c
c     Generates some particle data in sdf form.
c
c     Specifically, generates <np> particles randomly distributed on 
c     surface of sphere, and outputs <np> x 5 data where 2 fcns 
c     associated with (x,y,z) data are
c
c     1) max(abs(xj),abs(yj),abs(zj))
c     2) min(abs(xj),abs(yj),abs(zj))
c ======================================================================
      program      partdemo0

      implicit     none

      character*9  cdnm
      parameter  ( cdnm = 'partdemo0' )

      integer      iargc,  i4arg

      integer      np

      integer      npmax
      parameter  ( npmax = 10 000 000 )

      real*8       r(npmax,6)
      real*8       t

      if( iargc() .ne. 1 ) go to 900

      np = i4arg(1,-1)
      if( np .eq. -1 ) go to 900
      if( np .lt. 1  .or.  np .gt. npmax ) then
         write(0,*) 'cdnm: np=', np
         write(0,*) 'cdnm: Exceeds range 1 to ', npmax
         go to 900
      end if

      call genpart(r,np)
      t = 0.0d0 

      call gft_out_part_xyzf('partdemo0',t,r,np,3)

      stop

 900  continue
         write(0,*) 'usage: '//cdnm//' <np>'
      stop
      
      end

      subroutine genpart(r,np)
         implicit     none

         real*8       drand48

         integer      np
         real*8       r(np,6)

         integer      j
         real*8       xj, yj, zj, nrm

         call srand(np)

         do j = 1 , np 
            xj = (2.0d0 * drand48() - 1.0d0)
            yj = (2.0d0 * drand48() - 1.0d0)
            zj = (2.0d0 * drand48() - 1.0d0)
            nrm = 1.0d0 / sqrt(xj**2 + yj**2 + zj**2)
            xj = nrm * xj
            yj = nrm * yj
            zj = nrm * zj
            r(j,1) = xj
            r(j,2) = yj
            r(j,3) = zj
            r(j,4) = max(abs(xj),abs(yj),abs(zj))
            r(j,5) = min(abs(xj),abs(yj),abs(zj))
            r(j,6) = max(abs(xj) - abs(yj),abs(xj) - abs(zj),
     &                   abs(yj) - abs(zj))
         end do

         return

      end