program straight

      x=0.0
      y=0.0
      xold=x
      yold=y
      vx=1.0
      vy=0.0
      if(pgopen('/xwin')<=0)stop
      call pgenv(-2.0,2.0,-2.0,2.0,1,0)
      dt=0.0001
      do i=1, 1000000
        x = x + vx*dt
        y = y + vy*dt
        call pgbbuf
        call pgsci(0)
        call pgpt(1,xold,yold,20)
        call pgsci(1)
        call pgpt(1,x,y,20)
        call pgebuf
        xold=x
        yold=y
      enddo

      call pgclos
      end