Avoids doing two global MPI reduce ops in P2Function::getMaxMagnitude()

The initial implementation of P2Function::getMaxMagnitude() performs two
global MPI reduce operations. One in VertexDoFFunction::getMaxMagnitude()
and the second one in EdgeDoFFunction::getMaxMagnitude().

This commits adds to each of the above functions a second option parameter
bool mpiReduce, which defaults to true. P2Function::getMaxMagnitude()
invokes them with false and performs the global reduce itself.

We probably should do the same with P2Function::dot()?

src/tinyhhg_core/edgedofspace/EdgeDoFFunction.hpp

@@ -99,7 +99,7 @@ public:
   const PrimitiveDataID< FunctionMemory< ValueType >,   Edge>   & getEdgeDataID()   const { return edgeDataID_; }
   const PrimitiveDataID< FunctionMemory< ValueType >,   Face>   & getFaceDataID()   const { return faceDataID_; }
 
-  inline real_t getMaxMagnitude( uint_t level, DoFType flag = All );
+  inline real_t getMaxMagnitude( uint_t level, DoFType flag = All, bool mpiReduce = true );
 
 private:
 
@@ -305,7 +305,7 @@ inline void EdgeDoFFunction< ValueType >::enumerate_impl(uint_t level, uint_t& n
 
 
 template< typename ValueType >
-inline real_t EdgeDoFFunction< ValueType >::getMaxMagnitude( uint_t level, DoFType flag )
+inline real_t EdgeDoFFunction< ValueType >::getMaxMagnitude( uint_t level, DoFType flag, bool mpiReduce )
 {
   real_t localMax = real_t(0.0);
 
@@ -327,7 +327,11 @@ inline real_t EdgeDoFFunction< ValueType >::getMaxMagnitude( uint_t level, DoFTy
     }
   }
 
-  walberla::mpi::allReduceInplace( localMax, walberla::mpi::MAX, walberla::mpi::MPIManager::instance()->comm() );
+  if( mpiReduce )
+  {
+    walberla::mpi::allReduceInplace( localMax, walberla::mpi::MAX, walberla::mpi::MPIManager::instance()->comm() );
+  }
+
   return localMax;
 }
 

src/tinyhhg_core/p1functionspace/VertexDoFFunction.hpp

@@ -75,7 +75,7 @@ public:
   // TODO: write more general version(s)
   inline real_t getMaxValue( uint_t level, DoFType flag = All );
   inline real_t getMinValue( uint_t level, DoFType flag = All );
-  inline real_t getMaxMagnitude( uint_t level, DoFType flag = All );
+  inline real_t getMaxMagnitude( uint_t level, DoFType flag = All, bool mpiReduce = true );
 
   inline uint_t getNumLocalDoFs ( const uint_t & level ) const;
   inline uint_t getNumGlobalDoFs( const uint_t & level ) const;
@@ -626,7 +626,7 @@ inline real_t VertexDoFFunction< ValueType >::getMaxValue( uint_t level, DoFType
 
 
 template< typename ValueType >
-inline real_t VertexDoFFunction< ValueType >::getMaxMagnitude( uint_t level, DoFType flag )
+inline real_t VertexDoFFunction< ValueType >::getMaxMagnitude( uint_t level, DoFType flag, bool mpiReduce )
 {
   real_t localMax = real_t(0.0);
 
@@ -651,7 +651,10 @@ inline real_t VertexDoFFunction< ValueType >::getMaxMagnitude( uint_t level, DoF
     }
   }
 
-  real_t globalMax = walberla::mpi::allReduce( localMax, walberla::mpi::MAX );
+  real_t globalMax = localMax;
+  if( mpiReduce ) {
+    globalMax = walberla::mpi::allReduce( localMax, walberla::mpi::MAX );
+  }
 
   return globalMax;
 }

src/tinyhhg_core/p2functionspace/P2Function.hpp

@@ -395,8 +395,11 @@ class P2Function : public Function< P2Function< ValueType > >
   inline real_t getMaxMagnitude( uint_t level, DoFType flag = All )
   {
     real_t localMax = real_t(0.0);
-    localMax = std::max( localMax, vertexDoFFunction_->getMaxMagnitude( level, flag ) );
-    localMax = std::max( localMax, edgeDoFFunction_->getMaxMagnitude( level, flag ) );
+    localMax = std::max( localMax, vertexDoFFunction_->getMaxMagnitude( level, flag, false ) );
+    localMax = std::max( localMax, edgeDoFFunction_->getMaxMagnitude( level, flag, false ) );
+
+    walberla::mpi::allReduceInplace( localMax, walberla::mpi::MAX, walberla::mpi::MPIManager::instance()->comm() );
+
     return localMax;
   }