This guide helps you to upgrade from preCICE 2.x to preCICE 3.x.
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preCICE API

The following is a diff of how an adapter-port could look like. The guide continues underneath the code.

- #include "precice/SolverInterface.hpp"
+ #include "precice/precice.hpp"
  
  turnOnSolver(); //e.g. setup and partition mesh
  
- precice::SolverInterface participant("FluidSolver","precice-config.xml",rank,size); // constructor
+ precice::Participant     participant("FluidSolver","precice-config.xml",rank,size); // constructor
  
- const std::string& coric = precice::constants::actionReadIterationCheckpoint();
- const std::string& cowic = precice::constants::actionWriteIterationCheckpoint();
- const std::string& cowid = precice::constants::actionWriteInitialData();
  
- int dim = participant.getDimension();
+ int dim = participant.getMeshDimensions("FluidMesh");
- int meshID = precice.getMeshID("FluidMesh");

  int vertexSize; // number of vertices at wet surface
  // determine vertex count

  std::vector<double> coords(vertexSize*dim); // coords of vertices at wet surface
  // determine coordinates

  std::vector<int> vertexIDs(vertexSize);
- precice.setMeshVertices(meshID, vertexSize, coords.data(), vertexIDs.data());
+ precice.setMeshVertices("FluidMesh", coords, vertexIDs);
  
- int displID = precice.getDataID("Displacements", meshID);
- int forceID = precice.getDataID("Forces", meshID);
- std::vector<double> forces(vertexSize*dim);
- std::vector<double> displacements(vertexSize*dim);
+ const int forceDim = participant.getDataDimensions("FluidMesh", "Forces")
+ const int displDim = participant.getDataDimensions("FluidMesh", "Displacements")
+ std::vector<double> forces(vertexSize*forceDimn);
+ std::vector<double> displacements(vertexSize*displDim);
  
  double solverDt; // solver timestep size
  double preciceDt; // maximum precice timestep size
  double dt; // actual time step size
  
- preciceDt = participant.initialize();
- if (participant.isActionRequired(cowid)) {
-   participant.writeBlockVectorData(forceID, vertexSize, vertexIDs.data(), forces.data());
-   participant.markActionFulfilled(cowid);
- }
- participant.initializeData();
+ if (participant.requiresInitialData()) {
+   participant.writeData("FluidMesh", "Forces", vertexIDs, forces);
+ }
+ participant.initialize();
  
  while (participant.isCouplingOngoing()){
-   if(participant.isActionRequired(cowic)){
+   if(participant.requiresWritingCheckpoint()){
      saveOldState(); // save checkpoint
-     participant.markActionFulfilled(cowic);
    }
  
+   preciceDt = participant.getMaxTimeStepSize();
    solverDt = beginTimeStep(); // e.g. compute adaptive dt
    dt = min(preciceDt, solverDt);
  
-   participant.readBlockVectorData(displID, vertexSize, vertexIDs.data(), displacements.data());
+   participant.readData("FluidMesh", "Displacements", vertexIDs, dt, displacements);
    setDisplacements(displacements);
    solveTimeStep(dt);
    computeForces(forces);
-   participant.writeBlockVectorData(forceID, vertexSize, vertexIDs.data(), forces.data());
+   participant.writeData("FluidMesh", "Forces", vertexIDs, forces);
  
-   preciceDt = participant.advance(dt);
+   participant.advance(dt);
  
-   if (participant.isActionRequired(coric)) { // timestep not converged
+   if (participant.requiresReadingCheckpoint()) {
      reloadOldState(); // set variables back to checkpoint
-     participant.markActionFulfilled(coric);
    }
    else { // timestep converged
      endTimeStep(); // e.g. update variables, increment time
    }
  }
  participant.finalize(); // frees data structures and closes communication channels
  
  turnOffSolver();
  • The main preCICE header file and the main object was renamed. This means that you need to:
    • Replace #include "precice/SolverInterface.hpp" with #include "precice/precice.hpp".
    • Where declaring a preCICE object, replace the precice::SolverInterface type with precice::Participant.
    • Where constructing a preCICE object, replace the precice::SolverInterface( ... ) constructor with precice::Participant( ... ).
    • Consider renaming your objects from, e.g., interface to participant, to better reflect the purpose and to be consistent with the rest of the changes.
  • Steering methods
    • Replace double preciceDt = initialize() and double preciceDt = advance(dt) with initialize() and advance(dt), as they no longer have a return value.
    • Use double preciceDt = getMaxTimeStepSize(), where you need the max time step size or the relative end of the time window.
  • Dimensions
    • Replace getDimensions() with getMeshDimensions(meshName)
    • Replace any custom logic to determine the dimensionality of data with getDataDimensions(meshName, dataName)
  • Migrate from using mesh and data ids to directly using names
    • Remove the now obsolete calls to getMeshID() and getDataID() and any related variables / user-defined types.
    • Replace the use of mesh IDs with the mesh name.
    • Replace the use of data IDs with the respective mesh and data names (both are needed).
  • Migrate connectivity information to the vertex-only API. All setMeshX methods take vertex IDs as input and return nothing.
    • Directly define face elements or cells of your coupling mesh available in your solver by passing their vectices to preCICE, which automatically handles edges of triangles etc. See Mesh Connectivity for more information.
    • Rename setMeshTriangleWithEdges to setMeshTriangle and setMeshQuadWithEdges to setMeshQuad. The edge-based implementation was removed.
    • Use the new bulk functions to reduce sanitization overhead: setMeshEdges, setMeshTriangles, setMeshQuads, setMeshTetrahedra.
  • Implicit coupling
    • Remove precice::constants::actionReadIterationCheckpoint() and precice::constants::actionWriteIterationCheckpoint()
      • Replace isActionRequired() of the above actions with requiresReadingCheckpoint() or requiresWritingCheckpoint().
      • Remove markActionFulfilled() of the above actions. It is now implied that a requires*() is directly executed/fulfilled.
  • Migrate data access
    • Replace the commands to read data: readBlockVectorData, readVectorData, readBlockScalarData, readScalarData with the single command readData.
    • Replace the commands to write data: writeBlockVectorData, writeVectorData, writeBlockScalarData, writeScalarData with the single command writeData.
    • Replace the commands to write gradient data: writeBlockVectorGradientData, writeVectorGradientData, writeBlockScalarGradientData, writeScalarGradientData with the single command writeGradientData.
    • The signature of readData, writeData and writeGradientData has changed from const int*, const double*, and double* to precice::span<const VertexID>, precice::span<const double>, and span<double>. The sizes of passed spans are checked by preCICE. spans can be constructed using a pointer and size, or by a contigous container. Examples for the latter are std::vector, std:array, Eigen::VectorXd, and also std::span.
    • To simplify migration to readData(), use getMaxTimeStepSize() as relative read time for now to always read data at the end of the time window. Read up on time interpolation once you finished the port.
  • Migrate data initialization
    • Move the data initalization before the call to initialize(). You have to initialize the data if requiresInitialData() returns true.
    • Remove initializeData(). The function initializeData() has been merged into ìnitialize().
    • Remove precice::constants::actionWriteInitialData().
    • Remove markActionFulfilled() of write initial data.
    • Replace isActionRequired() of write initial data with requiresInitialData().
  • Rename the functions:
    • Replace getMeshVerticesAndIDs with getMeshVertexIDsAndCoordinates. Change the input argument meshID to meshName and swap the arguments for IDs and coordinates.
    • Replace isMeshConnectivityRequired with requiresMeshConnectivityFor. Instead of the input argument meshID, pass the meshName.
    • Replace isGradientDataRequired with requiresGradientDataFor. Instead of the input argument dataID, pass the meshName and dataName.
  • Remove the following without a replacement:
    • Remove mapWriteDataFrom() and mapReadDataTo() as custom timings were removed.
    • Remove hasMesh() and hasData() as there is no real usecase for them. All errors are unrecoverable.
    • Remove hasToEvaluateSurrogateModel() and hasToEvaluateFineModel() as they were stubs of a long-removed feature.
    • Remove getMeshVertices() and getMeshVertexIDsFromPositions(). This information is already known by the adapter. We docummented strategies on how to handle this in adapters.
    • Remove isReadDataAvailable() and isWriteDataRequired(). Due to time interpolation, writing generates samples in time, and reading is always possible between the current time and the end of the current time window.

Add relativeReadTime for all read data calls

The previously optional argument relativeReadTime is now mandatory for read data calls. This requires you to update all read data calls. See time interpolation for more details on this argument. If you don’t want to use subcycling or time interpolation, you can simply get the required relativeReadTime by calling double preciceDt = getMaxTimeStepSize() call. Change:

- couplingInterface.readBlockVectorData(meshName, dataReadName, numberOfVertices, vertexIDs.data(), readData.data());
+ preciceDt = participant.getMaxTimeStepSize();
+ participant.readData(meshName, dataReadName, vertexIDs, preciceDt, readData)

If you use subcycling, please do the following:

- couplingInterface.readBlockVectorData(meshName, dataReadName, numberOfVertices, vertexIDs.data(), readData.data());
+ preciceDt = participant.getMaxTimeStepSize();
  double dt = min(preciceDt, solverDt);
+ participant.readData(meshName, dataReadName, vertexIDs, dt, readData)

Remove initializeData() calls

The API function initializeData() has been removed in #1350. initialize() now takes care of all the initialization – including data initialization. This means, you have to call initialize(), where you previously called initializeData(). Be aware that this means that you have to write initial data before calling initialize(). Change:

- double dt = 0;
- dt        = couplingInterface.initialize();
  std::vector<double> writeData(dimensions, writeValue);

  // Write initial data before calling initialize()
-  const std::string & cowid = actionWriteInitialData();
-  if (couplingInterface.isActionRequired(cowid)) {
-    couplingInterface.writeVectorData(writeDataID, vertexIDs, writeData.data());
-    couplingInterface.markActionFulfilled(cowid);
+  if (participant.requiresInitialData()) {
+    participant.writeData(meshName, dataWriteName, vertexIDs, writeData);
  }

  // Move initialize to the place where you called initializeData() previously.
- couplingInterface.initializeData();
+ participant.initialize();
+ double dt = participant.getMaxTimeWindowSize();

Typical error message that should lead you here:

error: ‘class precice::Participant’ has no member named ‘initializeData’; did you mean ‘initialize’?
   63 |   participant.initializeData();
      |           ^~~~~~~~~~~~~~
      |           initialize

preCICE configuration file

  • The XML tag <solver-interface> was removed and all underlying functionality was moved to the <precice-configuration> tag. Remove the lines including <solver-interface> and </solver-interface>, and move any attributes (such as experimental) from the solver-interface to the precice-configuration tag. Move the sync-mode attribute to the new <profiling> tag (see below).
  • The dimensions configuration is now defined per mesh. Move the dimensions="2" or dimensions="3" from the <solver-interface> tag to each <mesh> tag: <mesh name="MeshOne" dimensions="3">.
  • Rename the <m2n: ... /> attributes from -> acceptor and to -> connector.

  • You can now add <profiling mode="all" /> after the <log> tag if you need full profiling data.

  • Participants
    • Replace <use-mesh provide="true" ... /> with <provide-mesh ... />, and <use-mesh provide="false" ... /> with <receive-mesh ... />.
    • Move and rename the optional attribute <read-data: ... waveform-order="1" /> to <data:scalar/vector ... waveform-degree="1".
    • Replace <export:vtk /> for parallel participants with <export:vtu /> or <export:vtp />.
    • Replace mapping constraint scaled-consistent with scaled-consistent-surface.
    • Remove all timings in the mapping configuration <mapping: ... timing="initial/onadvance/ondemand" />. preCICE now fully controls the mapping.
    • Remove the preallocations in the mapping configuration <mapping: ... preallocation="tree/compute/estimate/save/off" />. We always use the superior tree method.

    • Replace all RBF related <mapping:rbf-... /> tags. RBF mappings are now defined in terms of the applied solver (current options <mapping:rbf-global-direct ..., <mapping:rbf-global-iterative or <mapping:rbf-pum-direct ...) and the applied basis function as a subtag of the solver. Users should use the additionally added auto selection of an appropriate solver, which omits the solver specification, as follows:

        <mapping:rbf  ...>
    <basis-function:... />
  </mapping:rbf>

      Example:

      preCICE version 2 RBF configuration:

        <mapping:compact-polynomial-c0 direction="read" from= ... support-radius="0.3" />

      corresponding preCICE version 3 RBF configuration (using the recommended auto selection):

        <mapping:rbf  direction="read" from= ...>
    <basis-function:compact-polynomial-c0 support-radius="0.3" />
  </mapping:rbf>

      A specific solver should only be configured if you want to force preCICE to use and stick to a certain solver, independent of your problem size and execution.

    • Rename <mapping:rbf... use-qr-decomposition="true" /> to <mapping:rbf-global-direct ... > <basis-function:... /> </mapping:rbf-global-direct>.
    • We dropped quite some functionality concerning data actions as these were not used to the best of our knowledge and were hard to maintain:
      • Removed deprecated action timings regular-prior, regular-post, on-exchange-prior, and on-exchange-post.
      • Removed action timings read-mapping-prior, write-mapping-prior, and on-time-window-complete-post.
      • Removed ComputeCurvatureAction and ScaleByDtAction actions.
      • Removed callback functions vertexCallback and postAction from PythonAction interface.
      • Removed timewindowsize from the performAction signature of PythonAction. The new signature is performAction(time, data)
      • Using actions with multiple couping schemes and mixed time window sizes is not well defined!
  • Coupling schemes
    • Remove <extraplation-order value="..." /> in <coupling-scheme>. Contact us if you need this feature.
    • Replace <min-iteration-convergence-measure min-iterations="3" ... /> by <min-iterations value="3"/>. Not defining convergence measures leads to iterations until max-iterations is reached.
    • We removed the plain Broyden acceleration. You could use IQN-IMVJ instead, which is a multi-vector Broyden variant.

Building preCICE

Rename CMake configuration variables as follows:

  • PRECICE_PETScMapping -> PRECICE_FEATURE_PETSC_MAPPING
  • PRECICE_MPICommunication -> PRECICE_FEATURE_MPI_COMMUNICATION
  • PRECICE_Packages -> PRECICE_CONFIGURE_PACKAGE_GENERATION
  • PRECICE_PythonActions -> PRECICE_FEATURE_PYTHON_ACTIONS
  • PRECICE_ENABLE_C -> PRECICE_BINDINGS_C
  • PRECICE_ENABLE_FORTRAN ->PRECICE_BINDINGS_FORTRAN
  • PRECICE_ENABLE_LIBBACKTRACE -> PRECICE_FEATURE_LIBBACKTRACE_STACKTRACES

Language bindings

The renaming of the preCICE API from SolverInterface to preCICE also applies to all language bindings. The C++ header change precice/SolverInterface.hpp to precice/precice.hpp becomes:

  • In C: Replace #include "precice/SolverInterfaceC.h" with #include "precice/preciceC.h" and precicec_createSolverInterface( ... ) with precicec_createParticipant( ... ).
  • In Julia: Replace precicec_createSolverInterface( ... ) with precicec_createParticipant( ... ).
  • In Matlab: Replace SolverInterface with Participant everywhere.
  • In Fortran, Python: You don’t need to change anything.

Profiling

  • There are three profiling modes now: off, fundamental (default), all.
  • Add <profiling mode="all" /> inside the <precice-configuration> tag if you need detailed profiling data.
  • If you relied on sync-mode="on", remove it from <precice-configuration> and add it to the profiling tag <profiling synchronize="true" />.