Option to force regrid level zero (#3484)

## Summary
This PR gives the user an option to force regrid level zero.

## Additional background
This is needed for moving EB cases.

Src/Amr/AMReX_Amr.cpp

@@ -81,6 +81,7 @@ namespace
  bool plot_files_output;
  int checkpoint_nfiles;
  int regrid_on_restart;
+ int force_regrid_level_zero;
  int use_efficient_regrid;
  int plotfile_on_restart;
  int insitu_on_restart;
@@ -117,6 +118,7 @@ Amr::Initialize ()
  plot_files_output = true;
  checkpoint_nfiles = 64;
  regrid_on_restart = 0;
+ force_regrid_level_zero = 0;
  use_efficient_regrid = 0;
  plotfile_on_restart = 0;
  insitu_on_restart = 0;
@@ -254,6 +256,7 @@ Amr::InitAmr ()
  // Check for command line flags.
  //
  pp.queryAdd("regrid_on_restart",regrid_on_restart);
+ pp.queryAdd("force_regrid_level_zero",force_regrid_level_zero);
  pp.queryAdd("use_efficient_regrid",use_efficient_regrid);
  pp.queryAdd("plotfile_on_restart",plotfile_on_restart);
  pp.queryAdd("insitu_on_restart",insitu_on_restart);
@@ -1930,6 +1933,10 @@ Amr::timeStep (int level,
  // Update so that by default, we don't force a post-step regrid.
  amr_level[level]->setPostStepRegrid(0);
 
+ if(max_level==0 && force_regrid_level_zero){
+ regrid_level_0_on_restart();
+ }
+
  //
  // Allow regridding of level 0 calculation on restart.
  //
@@ -2580,6 +2587,10 @@ Amr::regrid (int lbase,
  bool regrid_level_zero = (!initial) && (lbase == 0)
  && ( loadbalance_with_workestimates || (new_grid_places[0] != amr_level[0]->boxArray()));
 
+ if(lbase==0 && force_regrid_level_zero){
+ regrid_level_zero = true;
+ }
+
  const int start = regrid_level_zero ? 0 : lbase+1;
 
  bool grids_unchanged = finest_level == new_finest;