program anim_sin
      implicit none
      real x(1000),y(1000),x_shift,dx,xold(1000),yold(1000)
      integer i,idummy,pgopen,j

      idummy=pgopen('/xwin')
      call pgenv(0.0-0.01,20.0+0.01,-3.0,3.0,0,0)

      dx=(20.0-0.0)/(1000-1)
      x_shift=0.0

      do i=1,1000
        xold(i)=x_shift+(i-1)*dx
        yold(i)=sin(x(i))
      end do

      do j=1,100000

        x_shift=x_shift+0.01
        do i=1,1000
c         x(i)=x_shift+(i-1)*dx
c         y(i)=sin(x(i))
          x(i)=(i-1)*dx
          y(i)=sin(x(i)-x_shift)
        end do
        call pgbbuf
        call pgsci(0)
        call pgline(1000,xold,yold)
        call pgsci(1)
        call pgline(1000,x,y)
        call pgebuf
        do i=1,1000
          xold(i)=x(i)
          yold(i)=y(i)
        end do

      end do

      call pgclos
      end