program circ_anim
      if(pgopen('/xwin')<=0)stop
      call pgenv(-2.0,2.,-2.,2.,1,0)
      call pgsfs(0)
      x=0.0
      y=0.0
      r=0.5
      xold=x
      yold=y
      rold=r
      do i=1,100000
        theta=i*0.0001
        r=0.5+0.2*sin(theta)
        call pgbbuf
        call pgsci(0)
        call pgcirc(xold,yold,rold)
        call pgsci(1)
        call pgcirc(x,y,r)
        call pgebuf
        xold=x
        yold=y
        rold=r
      end do
      end