program anim_circ
      implicit none
      real r,rold,theta,d_theta
      integer i, idummy, pgopen
      
      idummy = pgopen('/xwin')
      call pgenv(-5.0,5.0,-5.0,5.0,1,0)

      call pgsfs(2)
      r=2.0
      call pgcirc(0.0,0.0,r)

      rold=2.0

      d_theta=2*3.14159/3600
      theta=0
      do i=1,1000000
        theta = theta + d_theta
        r = 2.0 + sin(theta)
       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