subroutine chtmst(u,v,ek,dtin,cfl,nx,ny)
c*****************************************************************
c
c     impose the cfl condition on the time step and calculate the 
c     total kinetic energy.
c
c     dtin      ->    maximal time step
c     cfl       ->    cfl number
c     dt        <-    time step
c     ek        <-    total kinetic energy
c
c*****************************************************************
      integer i,j,nx,ny
      double precision u(nx,ny),v(nx,ny),
     +                 h,hinv,ek,dtin,cfl,uvmax,dt
      common/meshsz/h,hinv
      common/timest/dt
      uvmax = 0.D0
      ek    = 0.D0
      do 10 j=1,ny
      do 10 i=1,nx
         uvmax = dmax1(dabs(u(i,j)),dabs(v(i,j)),uvmax)
         ek    = ek + u(i,j)*u(i,j) + v(i,j)*v(i,j)
 10   continue
*
      ek = 0.5D0*ek*h*h
*     total kinetic energy

      if(uvmax .eq. 0.D0) then
         dt = dtin
      else
         dt = dmin1(dtin,cfl*h/uvmax)
      endif

      end