program dragged_fly_plot_again_dagger
      real m,k
      real daggerx(4),daggery(4)
      real daggerxold(4),daggeryold(4)
      real daggerxini(4),daggeryini(4)
      if(pgopen('/xwin')<=0)stop
      call pgenv(0.0,10.0,0.0,10.0,1,0)
 1000 write(*,*)'Vx ?'
      read(*,*)vx
      write(*,*)'Vy ?'
      read(*,*) vy
      write(*,*)'Mass ?'
      read(*,*)m
      write(*,*)'Air friction ?'
      read(*,*)k
      dt=0.000001
      x=0.0
      y=5.0
      daggerxini(1)=0.0
      daggeryini(1)=0.2
      daggerxini(2)=0.0
      daggeryini(2)=-0.2
      daggerxini(3)=1.0
      daggeryini(3)=0.0
      daggerxini(4)=0.0
      daggeryini(4)=0.2
  
      do while(y > 0.0)
        v=sqrt(vx*vx + vy*vy)
        f_d=(-1)*k*v
        ax_d=f_d*(vx/v)/m
        ay_d=f_d*(vy/v)/m
        ax=0.0 + ax_d
        ay=-9.8 + ay_d
        vx=vx+ax*dt
        vy=vy+ay*dt
        x=x+vx*dt
        y=y+vy*dt
        do i=1,4
c         daggerx(i)=x+daggerxini(i)*(vx/v)+daggeryini(i)*(vy/v)
c         daggery(i)=y+(-1)*daggerxini(i)*(vy/v)+daggeryini(i)*(vx/v)
          daggerx(i)=x+daggerxini(i)*(vx/v)+(-1)*daggeryini(i)*(vy/v)
          daggery(i)=y+daggerxini(i)*(vy/v)+daggeryini(i)*(vx/v)
        end do
c       call pgpt(1,x,y,20)
        call pgbbuf
        call pgsci(0)
        call pgline(4,daggerxold,daggeryold)
        call pgsci(1)
        call pgline(4,daggerx,daggery)
        call pgebuf
        do i=1,4
          daggerxold(i)=daggerx(i)
          daggeryold(i)=daggery(i)
        end do

      end do
      write(*,*)'Final hight :',y
      write(*,*)'Final distance :',x
      write(*,*)'Again?(1=yes,other=no)'
      read(*,*)i_again
      if(i_again==1)goto 1000
c     call pgclos
      end