program circle_animate
      if( pgopen('/xwin') <= 0 ) stop
      call pgenv(-1.0,1.0,-1.0,1.0,1,0)
      call pgsfs(0)

      rold=0.5
      x=0.0
      dx=0.001

      do i=1,100000
        x = x + dx
c       x = i*dx
        r = 0.5 + 0.1*sin(x)
        call pgbbuf
         call pgsci(0)
         call pgcirc(0.0,0.0,rold)
         call pgsci(1)
         call pgcirc(0.0,0.0,r)
        call pgebuf
        rold = r
      end do

      call pgclos
      end