New user input for grid type (collocated, staggered, hybrid) (#3683)

* Introduce `warpx.grid_type` parameter

* Replace `or` with `||`

* Update examples with new user input syntax

* Fix `if` condition

* Improve error message

* Fix `if` condition

* Fix bugs

* Fix warning

* Fix RZ

* Debugging

* Fix RZ

* Fix bug

* Clean up

* More changes:

- set default algo parameters with hybrid grid
- all hybrid input parameters under warpx name

* Set default field gathering algo for hybrid grids

* Update documentation

3 files changed, 18 insertions, 1 deletions

diff --git a/Source/Utils/RelativeCellPosition.cpp b/Source/Utils/RelativeCellPosition.cpp
index 55e933af0..1a108b54b 100644
--- a/Source/Utils/RelativeCellPosition.cpp
+++ b/Source/Utils/RelativeCellPosition.cpp
@@ -19,7 +19,7 @@ utils::getRelativeCellPosition(amrex::MultiFab const& mf)
 
     // amrex::CellIndex::CELL means: 0.5 from lower corner for that index/direction
     // amrex::CellIndex::NODE means: at corner for that index/direction
-    // WarpX::do_nodal means: all indices/directions on CellIndex::NODE
+    // WarpX::grid_type==GridType::Collocated means: all indices/directions on CellIndex::NODE
     for (int d = 0; d < AMREX_SPACEDIM; d++)
     {
         if (idx_type.cellCentered(d))
diff --git a/Source/Utils/WarpXAlgorithmSelection.H b/Source/Utils/WarpXAlgorithmSelection.H
index fe90cb196..d0d8678f5 100644
--- a/Source/Utils/WarpXAlgorithmSelection.H
+++ b/Source/Utils/WarpXAlgorithmSelection.H
@@ -36,6 +36,14 @@ struct MacroscopicSolverAlgo {
     };
 };
 
+struct GridType {
+    enum {
+        Collocated = 0,
+        Staggered = 1,
+        Hybrid = 2
+    };
+};
+
 struct ElectromagneticSolverAlgo {
     enum {
         None = 0,
diff --git a/Source/Utils/WarpXAlgorithmSelection.cpp b/Source/Utils/WarpXAlgorithmSelection.cpp
index d3b5f5e43..99c068fc0 100644
--- a/Source/Utils/WarpXAlgorithmSelection.cpp
+++ b/Source/Utils/WarpXAlgorithmSelection.cpp
@@ -22,6 +22,13 @@
 // Define dictionary with correspondance between user-input strings,
 // and corresponding integer for use inside the code
 
+const std::map<std::string, int> grid_to_int = {
+    {"collocated", GridType::Collocated},
+    {"staggered", GridType::Staggered},
+    {"hybrid", GridType::Hybrid},
+    {"default", GridType::Staggered}
+};
+
 const std::map<std::string, int> electromagnetic_solver_algo_to_int = {
     {"none",    ElectromagneticSolverAlgo::None },
     {"yee",     ElectromagneticSolverAlgo::Yee },
@@ -140,6 +147,8 @@ GetAlgorithmInteger( amrex::ParmParse& pp, const char* pp_search_key ){
     std::map<std::string, int> algo_to_int;
     if (0 == std::strcmp(pp_search_key, "maxwell_solver")) {
         algo_to_int = electromagnetic_solver_algo_to_int;
+    } else if (0 == std::strcmp(pp_search_key, "grid_type")) {
+        algo_to_int = grid_to_int;
     } else if (0 == std::strcmp(pp_search_key, "do_electrostatic")) {
         algo_to_int = electrostatic_solver_algo_to_int;
     } else if (0 == std::strcmp(pp_search_key, "particle_pusher")) {