program circle_anim
      if( pgopen('/xwin') <= 0 ) stop

      call pgenv(-4.0,4.0,-4.0,4.0,1,0)
      call pgsfs(2)
      x=0.0
      y=0.0
      r=2.0
      rold=r
      dtheta=0.0001
      do i=1,100000
        theta = (i-1)*dtheta
        r=2.0+0.5*sin(theta)
       call pgbbuf
        call pgsci(0)
        call pgcirc(x,y,rold)
        call pgsci(1)
        call pgcirc(x,y,r)
       call pgebuf
        rold = r
      end do

c     call pgcirc(x,y,r)

      call pgclos
      end