Different behaviou of setMeshQuads() between v3.1.2 and v3.2.0 in setting 2D mesh connectivity

Using preCICE
1 
  <mesh name="A-Mesh" dimensions="2">
    <use-data name="etaHOS" />
    <use-data name="UHOS" />
  </mesh>

  <mesh name="B-Mesh" dimensions="2">
    <use-data name="etaHOS" />
    <use-data name="UHOS" />
  </mesh>

  <participant name="A">
    <provide-mesh name="A-Mesh" />
    <receive-mesh name="B-Mesh" from="B" />
    <read-data name="etaHOS" mesh="A-Mesh" />
    <read-data name="UHOS" mesh="A-Mesh" />
    <mapping:linear-cell-interpolation direction="read" from="B-Mesh" to="A-Mesh" constraint="consistent" />
  </participant>

  <participant name="B">
    <provide-mesh name="B-Mesh" />
    <write-data name="etaHOS" mesh="B-Mesh" />
    <write-data name="UHOS" mesh="B-Mesh" />
  </participant>

As shown above, pure 2D coupling ({x0, y0,x1, y1,x2, y2,… …, xn, yn} passed to precicef_set_vertices()), to satisfy mapping:linear-cell-interpolation, precicef_set_mesh_quads() is called to build connectivities for Mesh-B. But got the following error in v3.2.0. It works fine in v3.1.2. Wondering if there’s any un-documented change in behavious of the precicef_set_mesh_quads() function. How can I get around this? Many thanks.

ASSERTION FAILED
Location:   precice::math::geometry::ConvexityResult precice::math::geometry::isConvexQuad(std::array<Eigen::Matrix<double, -1, 1>, 4>)
File:       /scratcha-fdgs/lux/OpenFOAM/lux-v2106/platforms/precice-3.2.0/src/math/geometry.cpp:149
Expression: std::all_of(coords.cbegin(), coords.cend(), [](const auto &v) { return v.size() == 3; })
Rank:       0
Arguments:
  0: "This only works in 3D." == This only works in 3D.

Stacktrace:
 0# 0x00007FC652F4458C in /scratcha-fdgs/lux/OpenFOAM/lux-v2106/platforms/precice-3.2.0/platforms/lib64/libprecice.so.3
 1# 0x00007FC65272779B in /scratcha-fdgs/lux/OpenFOAM/lux-v2106/platforms/precice-3.2.0/platforms/lib64/libprecice.so.3
 2# 0x00007FC652E8DADA in /scratcha-fdgs/lux/OpenFOAM/lux-v2106/platforms/precice-3.2.0/platforms/lib64/libprecice.so.3
 3# precice::Participant::setMeshQuads(precice::span<char const, 18446744073709551615ul>, precice::span<int const, 18446744073709551615ul>) in /scratcha-fdgs/lux/OpenFOAM/lux-v2106/platforms/precice-3.2.0/platforms/lib64/libprecice.so.3
 4# precicef_set_mesh_quads_ in /scratcha-fdgs/lux/OpenFOAM/lux-v2106/platforms/precice-3.2.0/platforms/lib64/libprecice.so.3
2

For 3D cases, where precicef_set_mesh_tetrahedra() is called, the code works fine both in v3.1.2 and v3.2.0.

3

@Makis After digging into the source code, found that in setMeshQuads(), there’s a line:

    auto convexity = math::geometry::isConvexQuad(coords);

at beginning of which is:

  PRECICE_ASSERT(std::all_of(coords.cbegin(), coords.cend(),
                             [](const auto &v) { return v.size() == 3; }),
                 "This only works in 3D.");

Guess this assert will call std::abort() if dim != 3 in Degub mode, which is unfortunate my case. And previously in v3.1.2 I am only running in Release mode, that is why I didn’t get error.

My question is, my earlier runs in v3.1.2 showed me that precice works fine when I call setMeshQuads() for pure 2D cases, why in the above PRECICE_ASSERT it is said “This only works in 3D”? My use case is 2D volume coupling, and I quote your document “For volume coupling in 2D, mesh connectivity boils down to defining triangles and / or quads between vertices”.

4

Rebuild with Release mode, got another error from same function call (math::geometry::isConvexQuad(coords)):

---[precice] ERROR:  Non-planar quads are not supported. The vertex coordinates are: [312.5,2.55, 375,2.55, 375,3.825, 312.5,3.825].

This is not happening in v3.1.2. The difference in configuring v3.1.2 and v3.2.0 is just replaced boost 1.82.0 to 1.86.0. same eigen lib.

5

made following change to the precice code, now it works. Hope this will not break the precice internal logic.

ConvexityResult isConvexQuad(std::array<Eigen::VectorXd, 4> coords)
{
  // Ensure all points have at least 2 or 3 dimensions
  PRECICE_ASSERT(std::all_of(coords.cbegin(), coords.cend(),
                             [](const auto& v) {
                               return v.size() == 2 || v.size() == 3;
                             }),
                 "All coordinates must be 2D or 3D.");

  // If coords are 2D, extend them to 3D by adding a zero z-component
  if (coords[0].size() == 2) {
    for (auto& v : coords) {
      Eigen::VectorXd extended(3);
      extended << v[0], v[1], 0.0;
      v = extended;
    }
  }

  // Now ensure all vectors are 3D
  PRECICE_ASSERT(std::all_of(coords.cbegin(), coords.cend(),
                             [](const auto& v) { return v.size() == 3; }),
                 "This only works in 3D.");

  // ...The rest remains the same...
}
6

so far the tests are normal.

7

Hi,
This definitely a bug in preCICE.
Quads were never designed to be used in 2D, which changed with the introduction of the linear cell interpolation mapping.

Thanks for doing the research! I opened an issue:

Best
Frédéric