program plot_sin
      if(pgopen('/xwin')<=0)stop
      call pgenv(0.0,20.0,-1.5,1.5,0,0)
      open(unit=20,file='data1.dat')
      read(20,*)n
      do i=1,n
        read(20,*)x,y
        call pgpt(1,x,y,1)
      enddo
      call pgclos
      end