program fly_drag_plot
      real k,m
      if(pgopen('/xwin')<=0)stop
      call pgenv(0.0,5.0,0.0,5.0,1,0)
 1000 write(*,*)'Initial Vx?'
      read(*,*) vx
      write(*,*)'Initial Vy?'
      read(*,*) vy
      write(*,*) 'Air drag coeff k?'
      read(*,*) k
      write(*,*) 'Mass?'
      read(*,*) m
      dt = 0.001
      x = 0.0
      y = 1.0
      do while (y >= 0.0)

        v = sqrt(vx*vx + vy*vy)
        fd = -1*k*v
        fdx = fd*vx/v
        fdy = fd*vy/v
        ax = fdx/m
        ay = fdy/m - 9.8

        x = x + vx*dt
        y = y + vy*dt
        vx = vx + ax*dt
        vy = vy + ay*dt
        call pgpt(1,x,y,20)
      end do
      write(*,*)'Distance is',x,'Hight is',y
      write(*,*)'Again? (0=stop, *any value*=again)'
      read(*,*)i
      if (i==0) stop
      goto 1000
      end