/*@@
   @file      Courant.c
   @date      September 4 1999
   @author    Gabrielle Allen
   @desc
              Specification of timestep using Courant condition
   @enddesc
 @@*/

#include <math.h>
#include <stdlib.h>

#include <cctk.h>
#include <cctk_Arguments.h>
#include <cctk_Parameters.h>


void Time_Courant(CCTK_ARGUMENTS)
{
  DECLARE_CCTK_PARAMETERS;
  DECLARE_CCTK_ARGUMENTS;


  /* Calculate the minimum grid spacing */
  CCTK_REAL min_spacing = cctk_delta_space[0];

  if (cctk_dim>=2)
  {
    min_spacing = (min_spacing<cctk_delta_space[1] ?
        min_spacing : cctk_delta_space[1]);
  }

  if (cctk_dim>=3)
  {
    min_spacing = (min_spacing<cctk_delta_space[2] ?
        min_spacing : cctk_delta_space[2]);
  }

  if (cctk_dim>=4)
  {
    CCTK_WARN(0,"Time Step not defined for greater than 4 dimensions");
  }

  /* Calculate the courant timestep */
  if (CCTK_Equals(timestep_method,"courant_time"))
  {
    *courant_dt = courant_fac*(*courant_min_time)/sqrt((double)cctk_dim);
  }
  else if (CCTK_Equals(timestep_method,"courant_speed"))
  {
    *courant_dt = courant_fac*min_spacing/
      (*courant_wave_speed)/sqrt((double) cctk_dim);
  }

   if (CCTK_Equals(terminate, "time")||CCTK_Equals(terminate, "both"))
   {
     if (cctkGH->cctk_time + *courant_dt > cctk_final_time)
     {
       *courant_dt = (1 + 1.e-10) * (cctk_final_time - cctkGH->cctk_time);
     }
   }

  /* Set the Cactus timestep */

  if (!timestep_outonly)
  {
    cctkGH->cctk_delta_time = *courant_dt;
    if (verbose)
    {
      CCTK_VInfo(CCTK_THORNSTRING,"Time step set to %g",CCTK_DELTA_TIME);
    }
  }
  else
  {
    cctkGH->cctk_delta_time = dtfac*min_spacing;
    if (cctkGH->cctk_iteration % timestep_outevery == 0)
    {
      CCTK_VInfo(CCTK_THORNSTRING,"Courant timestep would be %g",*courant_dt);
    }
  }
}