Add periodicIndexSpace analogous to boundaryIndexSpace

grid/src/Cabana_Grid_LocalGrid.hpp

@@ -254,9 +254,9 @@ class LocalGrid
 
   private:
     // Helper functions
-    zeroIndexSpace();
-    setupHaloWidthImpl( const int halo_width );
-    checkOffsets( const std::array<int, num_space_dim>& off_ijk );
+    auto zeroIndexSpace();
+    auto setupHaloWidth( const int halo_width );
+    void checkOffsets( const std::array<int, num_space_dim>& off_ijk );
 
     template <class OwnedIndexSpace>
     auto getBound( OwnedIndexSpace owned_space, const int upper_lower,

grid/src/Cabana_Grid_LocalGrid_impl.hpp

@@ -116,7 +116,7 @@ auto LocalGrid<MeshType>::setupHaloWidth( const int halo_width )
     return hw;
 }
 
-auto LocalGrid<MeshType>::checkOffsets(
+void LocalGrid<MeshType>::checkOffsets(
     const std::array<int, num_space_dim>& off_ijk )
 {
     // Check that the offsets are valid.
@@ -238,6 +238,42 @@ LocalGrid<MeshType>::boundaryIndexSpace( DecompositionTag t1, EntityType t2,
     return boundaryIndexSpace( t1, t2, off_ijk, halo_width );
 }
 
+//---------------------------------------------------------------------------//
+// Given the relative offsets of a boundary relative to this local grid's
+// indices get the set of local entity indices associated with that periodic
+// boundary in the given decomposition. Optionally provide a halo width for the
+// shared space. This halo width must be less than or equal to the halo width of
+// the local grid. The default behavior is to use the halo width of the local
+// grid. For example, if the Own decomposition is used, the interior entities
+// that would be affected by a periodic boundary operation are provided whereas
+// if the Ghost decomposition is used the halo entities on the boundary are
+// provided.
+template <class MeshType>
+template <class DecompositionTag, class EntityType>
+auto LocalGrid<MeshType>::periodicIndexSpace(
+    DecompositionTag t1, EntityType t2,
+    const std::array<int, num_space_dim>& off_ijk, const int halo_width ) const
+    -> IndexSpace<num_space_dim>
+{
+    auto hw = setupHaloWidth( halo_width );
+    checkOffsets( off_ijk );
+
+    // Check to see if this is a periodic neighbor. If not, return a boundary
+    // space of size 0 because there is no periodic boundary.
+    bool periodic_ijk = true;
+    for ( std::size_t d = 0; d < num_space_dim; ++d )
+        if ( off_ijk[d] == 0 || !_global_grid->isPeriodic( d ) )
+            periodic_ijk = false;
+    if ( !periodic_ijk )
+    {
+        return zeroIndexSpace();
+    }
+
+    // Periodic spaces equivalent to boundary except determining whether this
+    // offset is valid (see above).
+    return boundaryIndexSpaceImpl( t1, t2, off_ijk, hw );
+}
+
 //---------------------------------------------------------------------------//
 // Get the local index space of the owned cells.
 template <class MeshType>