region Mask question

ddrake
Topic Author
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4 years 1 month ago - 4 years 1 month ago #3204 by ddrake

region Mask question was created by ddrake

in Python, I can create and save a mesh with two regions like this:

Code:

geo = SplineGeometry()
geo.AddRectangle((0,0), (2,2),
                 bcs=["b","r","t","l"],
                 leftdomain=1)
geo.AddRectangle((1,0.9), (1.3,1.4),
                 bcs=["b2","r2","t2","l2"],
                 leftdomain=2, rightdomain=1)
geo.SetMaterial (1, "outer")
geo.SetMaterial (2, "inner")
mesh = Mesh(geo.GenerateMesh(maxh=0.1))
mesh.ngmesh.Save("mesh2.vol")

Now I can load the mesh and get its materials and see that their masks are correct

Code:

mesh = Mesh("mesh2.vol")
mesh.GetMaterials()
>> ('outer', 'inner')
print(mesh.Materials("inner").Mask())
>> 0: 01 # Correct
print(mesh.Materials("outer").Mask())
>> 0: 10  # Correct

The Pybind bindings in python_comp_mesh.cpp are like this:

Code:

py::class_<MeshAccess, shared_ptr<MeshAccess>> mesh_access(m, "Mesh",
    ...
    .def("GetMaterials",
         [](const MeshAccess & ma)
         {
           return MakePyTuple(ma.GetMaterials(VOL));
         },
         "Return list of material names")

    .def("Materials",
         [](const shared_ptr<MeshAccess> & ma, string pattern)
          {
            return Region (ma, VOL, pattern);
          },
         py::arg("pattern"),
         docu_string("Return mesh-region matching the given regex pattern"))

  py::class_<Region> (m, "Region", "a subset of volume or boundary elements")
   ...
    .def("Mask",[](Region & reg)->BitArray { return reg.Mask(); }, "BitArray mask of the region")

Now if I try to do the same in C++ that I did in Python

Code:

//  ngscxx -c mask_test.cpp  ; ngsld mask_test.o -lngcomp -lngcore -lmesh
#include <solve.hpp>
using namespace ngsolve;
int main(int argc, char** argv)
{
  auto ma = make_shared<MeshAccess>("mesh2.vol");
  cout << ma->GetMaterials(VOL) << endl;
  // correctly prints: 0:outer  1:inner
  int nreg = ma->GetNRegions(VOL);
  cout  nreg << endl;
  // correctly prints: 2
  auto inner = Region(ma, VOL, "inner");
  auto outer = Region(ma, VOL, "outer");
  cout << inner.Mask() << endl;

// 0: 11 // Wrong!!!

Code:

  cout << outer.Mask() << endl;

// 0: 11 // Wrong!!!

Code:

  return 0;
}

Some of our C++ code similiar to this example worked until an NGSolve update about a week ago (or maybe a month ago).

Best,
Dow

Last edit: 4 years 1 month ago by ddrake. Reason: clarification

joachim
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Administrator

4 years 1 month ago #3205 by joachim

Replied by joachim on topic region Mask question

Hi Dow,

there is now a new Region - constructor with the third argument a bool.

The char* is converted to the bool and not to the string.

it works if you write:

auto inner = Region(ma, VOL, string("inner"));

That's a dangerous pitfall, think we should get rid of the new ctor.

Joachim

The following user(s) said Thank You: ddrake

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