Use FwdTrans instead of `FwdTransLocalElmt` for Parareal iteration in time-integration

CHANGELOG.md

@@ -13,6 +13,7 @@ v5.6.0
 - Enable varcoeffs for Collections (!1701)
 - Fix misplaced " in Nektar++Config.cmake (!1742)
 - Further tidy-up in linear solver (!1761)
+- Use FwdTrans in UnsteadySystem when using Parareal (!1785)
 - Automate deployment of README.md to dockerhub (!1786)
 
 **CompressibleFlowSolver**

library/SolverUtils/Driver.cpp

@@ -77,14 +77,6 @@ Driver::Driver(const LibUtilities::SessionReaderSharedPtr pSession,
 {
 }
 
-/**
- *
- */
-Driver::~Driver()
-
-{
-}
-
 /**
  *
  */

library/SolverUtils/Driver.h

@@ -65,7 +65,7 @@ class Driver
 {
 public:
     /// Destructor
-    virtual ~Driver();
+    virtual ~Driver() = default;
 
     /// Initialise Object
     SOLVER_UTILS_EXPORT inline void InitObject(std::ostream &out = std::cout);

library/SolverUtils/DriverParallelInTime.cpp

@@ -643,12 +643,6 @@ void DriverParallelInTime::Interpolate(
         // If different polynomial orders, interpolate solution.
         else
         {
-            // Assign memory for coefficient space.
-            Array<OneD, NekDouble> incoeff(infield[n]->GetNcoeffs());
-
-            // Transform solution from physical to coefficient space.
-            infield[n]->FwdTransLocalElmt(inphys, incoeff);
-
             for (size_t i = 0; i < infield[n]->GetExpSize(); ++i)
             {
                 // Get the elements.
@@ -656,11 +650,14 @@ void DriverParallelInTime::Interpolate(
                 auto outElmt = outfield[n]->GetExp(i);
 
                 // Get the offset of elements in the storage arrays.
-                size_t inoffset  = infield[n]->GetCoeff_Offset(i);
+                size_t inoffset  = infield[n]->GetPhys_Offset(i);
                 size_t outoffset = outfield[n]->GetPhys_Offset(i);
 
+                // Transform solution from physical to coefficient space.
+                Array<OneD, NekDouble> incoeff(inElmt->GetNcoeffs());
+                inElmt->FwdTrans(inphys + inoffset, incoeff);
+
                 // Interpolate elements.
-                Array<OneD, NekDouble> tmp;
                 StdRegions::StdExpansionSharedPtr expPtr;
                 if (inElmt->DetShapeType() == LibUtilities::Seg)
                 {
@@ -758,7 +755,10 @@ void DriverParallelInTime::Interpolate(
                             inElmt->GetBasis(2)->GetNumModes(),
                             outElmt->GetBasis(2)->GetPointsKey()));
                 }
-                expPtr->BwdTrans(incoeff + inoffset, tmp = outphys + outoffset);
+
+                // Transform solution from coefficient to physical space.
+                Array<OneD, NekDouble> tmp = outphys + outoffset;
+                expPtr->BwdTrans(incoeff, tmp);
             }
         }
     }

library/SolverUtils/UnsteadySystem.cpp

@@ -384,9 +384,18 @@ void UnsteadySystem::v_DoSolve()
                 fields[i] = m_fields[m_intVariables[i]]->UpdatePhys();
                 if (v_RequireFwdTrans())
                 {
-                    m_fields[m_intVariables[i]]->FwdTransLocalElmt(
-                        m_fields[m_intVariables[i]]->GetPhys(),
-                        m_fields[m_intVariables[i]]->UpdateCoeffs());
+                    if (m_comm->IsParallelInTime())
+                    {
+                        m_fields[m_intVariables[i]]->FwdTrans(
+                            m_fields[m_intVariables[i]]->GetPhys(),
+                            m_fields[m_intVariables[i]]->UpdateCoeffs());
+                    }
+                    else
+                    {
+                        m_fields[m_intVariables[i]]->FwdTransLocalElmt(
+                            m_fields[m_intVariables[i]]->GetPhys(),
+                            m_fields[m_intVariables[i]]->UpdateCoeffs());
+                    }
                 }
                 m_fields[m_intVariables[i]]->SetPhysState(false);
             }