subroutine timest(vf,uf,curv,n,dtin,dt)
*     ******************************************************
*     determine the time step allowed based on the
*     velocity and the curvature.
*     ******************************************************
      integer n,j
      double precision vf(0:8192),uf(0:8192),curv(0:8192)
      double precision dtin,dt,cfl,vmax,cmax,sa,pi,p2,vm
      common/salpha/sa
      common/valupi/pi,p2
      parameter (cfl=0.5D0)
      vmax = 0.D0
      cmax = 0.D0        
      do 10 j=1,n
         vm = dsqrt(vf(j)*vf(j)+uf(j)*uf(j))
         vmax = dmax1(vm,vmax)
         cmax = dmax1(dabs(curv(j)),cmax)
 10   continue
      dt = dmin1( dtin,
     +     cfl/vmax*dmin1(p2*sa/dfloat(n), 1.D0/cmax) )
      end