c  Mahc_Evolve: Numerical Evolution of the General Relativistic Hydro Equations
c  Copyright (C) 2001 Mark Miller

/*@@
  @file      Mahc_pred_calc_update.F
  @date      December 1999
  @author    Mark Miller
  @desc
     Calculate the hydro update for the predictor step.
  @enddesc
@@*/

#include "cctk.h"
#include "cctk_Parameters.h"
#include "cctk_Arguments.h"


/*@@
  @routine    Mahc_pred_calc_update
  @date       December 1999
  @author     Mark Miller
  @desc
     Calculate the hydro update for the predictor step.
  @enddesc
  @calls
  @calledby
  @history
  @endhistory
@@*/

      subroutine Mahc_pred_calc_update(CCTK_FARGUMENTS)
      implicit none
      DECLARE_CCTK_FARGUMENTS
      DECLARE_CCTK_PARAMETERS


      CCTK_REAL evolve_dt
      integer order,didit,CCTK_Equals

c     Cactus just did timelevel rotation, so we must now populate the new
c     evolved variables:
      dens = dens_p
      sx   = sx_p
      sy   = sy_p
      sz   = sz_p
      tau  = tau_p

      didit = 0
      evolve_dt = cctk_delta_time

      order = -1
      if (CCTK_EQUALS(hydro_order,'fluxlim')) then
         order = 2
      endif
      if (CCTK_EQUALS(hydro_order,'upwind')) then
         order = 1
      endif
      if(order .eq. -1) then
         write(*,*) 'Mahc_pred_calc_update: error: hydro_order must '
         write(*,*) '   contain fluxlim (2nd order) or '
         write(*,*) '   upwind (1st order) '
         call CCTK_WARN(0,"Must set hydro_order to something reasonable!")
      endif

      if((CCTK_EQUALS(hydro_method,'fluxsplit')) .or.
     .   (CCTK_EQUALS(hydro_method,'roe'))) then

      didit = 1

c     zero out the flux contributions:
      del_dens = 0.0d0
      del_sx   = 0.0d0
      del_sy   = 0.0d0
      del_sz   = 0.0d0
      del_tau  = 0.0d0

c     calculate the hydro flux updates
      if(CCTK_EQUALS(hydro_method,'fluxsplit')) then
c        call fluxsplit_x_update(MAHC_ARGS,evolve_dt,order)
c        call fluxsplit_y_update(MAHC_ARGS,evolve_dt,order)
c        call fluxsplit_z_update(MAHC_ARGS,evolve_dt,order)
         call CCTK_WARN(0,"got to hook up fluxsplit!")
      endif
      if((CCTK_EQUALS(hydro_method,'roe')).or.
     .   (CCTK_EQUALS(hydro_method,'eno'))) then
         call roe_flux_x_update(CCTK_FARGUMENTS,evolve_dt,order)
         call roe_flux_y_update(CCTK_FARGUMENTS,evolve_dt,order)
         call roe_flux_z_update(CCTK_FARGUMENTS,evolve_dt,order)
      endif
  
c     calculate the hydro source updates
      call hydro_source_update(CCTK_FARGUMENTS,evolve_dt)

      endif

      return
      end