program anim_circ
      idummy=pgopen('/xwin')
      call pgenv(-10.0,10.0,-10.0,10.0,1,0)

      call pgsfs(2)

      d_theta=2*3.14/3600
      theta = 0.0
      rold=2.0
      do i=1,100000
        theta = theta + d_theta

        r = 3.0 + sin(theta)

        call pgsci(0)
        call pgcirc(0.0,0.0,rold)
        call pgsci(1)
        call pgcirc(0.0,0.0,r)
        rold=r
      end do

      call pgclos
      end