!     copyright:wangaifeng 
!     DATE     :2007-07-25
!     Company  :GUCAS
      real function CFL(u,dx,dy,nx,ny,ighost,gama)
      implicit real(a-h,o-z)      
	real u(-ighost:nx+ighost,-ighost:ny+ighost,0:3)
      
      dmaxvel=1e-10
	do i=1,nx
	do j=1,ny
	uu=u(i,j,1)/u(i,j,0)
	vv=u(i,j,2)/u(i,j,0)
	p=(gama-1)*(u(i,j,3)-0.5*u(i,j,0)*(uu**2+vv**2))
	vel=sqrt(gama*p/u(i,j,0))+sqrt(uu**2+vv**2)
	if(vel.gt.dmaxvel) dmaxvel=vel
	enddo
	enddo

	CFL=0.1*min(dx,dy)/dmaxvel
	end