program circle_animate_xy
      if( pgopen('/xwin') <= 0 ) stop
      call pgenv(-1.0,1.0,-1.0,1.0,1,0)
      call pgsfs(0)
      xold=0.0
      yold=0.0
      rold=0.5
      t=0.0
      x=0.0
      y=0.0
      dt=0.001

      do i=1,100000
        t = t + dt
        x = 0.3*sin(0.3*t)
        r = 0.5 + 0.1*sin(t)
        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

      call pgclos
      end