# MatrixMathFilter

VTKExamples/Cxx/Meshes/MatrixMathFilter

### Code

MatrixMathFilter.cxx

    #include <vtkSmartPointer.h>
    #include <vtkPointData.h>
    #include <vtkSphereSource.h>
    #include <vtkMatrixMathFilter.h>
    #include <vtkPolyDataMapper.h>
    #include <vtkActor.h>
    #include <vtkRenderWindow.h>
    #include <vtkRenderer.h>
    #include <vtkRenderWindowInteractor.h>
    #include <vtkUnstructuredGridReader.h>
    #include <vtkDataSetSurfaceFilter.h>
    #include <vtkXMLUnstructuredGridWriter.h>
    #include <vtkXMLPolyDataWriter.h>

    int main(int argc, char *argv[])
    {
      if(argc < 2)
      {
        std::cerr << "Required arguments: vtkFile" << std::endl;
        return EXIT_FAILURE;
      }

      std::string filename = argv[1]; // "/Data/tensors.vtk";

      std::cout << "filename: " << filename << std::endl;

      vtkSmartPointer<vtkUnstructuredGridReader> reader =
        vtkSmartPointer<vtkUnstructuredGridReader>::New();
      reader->SetFileName(filename.c_str());
      reader->Update();

      vtkSmartPointer<vtkDataSetSurfaceFilter> surfaceFilter =
        vtkSmartPointer<vtkDataSetSurfaceFilter>::New();
      surfaceFilter->SetInputConnection(reader->GetOutputPort());
      surfaceFilter->Update();

      vtkSmartPointer<vtkMatrixMathFilter> matrixMathFilter =
        vtkSmartPointer<vtkMatrixMathFilter>::New();
      //matrixMathFilter->SetOperationToDeterminant();
      matrixMathFilter->SetOperationToEigenvalue();
      matrixMathFilter->SetInputConnection(surfaceFilter->GetOutputPort());
      matrixMathFilter->Update();
      matrixMathFilter->GetOutput()->GetPointData()->SetActiveScalars("Eigenvalue");

      vtkSmartPointer<vtkXMLPolyDataWriter> writer = vtkSmartPointer<vtkXMLPolyDataWriter>::New();
      writer->SetInputConnection(matrixMathFilter->GetOutputPort());
      writer->SetFileName("output.vtp");
      writer->Write();

      // Visualize
      vtkSmartPointer<vtkPolyDataMapper> mapper = vtkSmartPointer<vtkPolyDataMapper>::New();
      mapper->SetInputConnection(matrixMathFilter->GetOutputPort());

      vtkSmartPointer<vtkActor> actor = vtkSmartPointer<vtkActor>::New();
      actor->SetMapper(mapper);

      vtkSmartPointer<vtkRenderer> renderer = vtkSmartPointer<vtkRenderer>::New();
      vtkSmartPointer<vtkRenderWindow> renderWindow = vtkSmartPointer<vtkRenderWindow>::New();
      renderWindow->AddRenderer(renderer);
      vtkSmartPointer<vtkRenderWindowInteractor> renderWindowInteractor =
        vtkSmartPointer<vtkRenderWindowInteractor>::New();
      renderWindowInteractor->SetRenderWindow(renderWindow);

      renderer->AddActor(actor);
      renderer->SetBackground(.3, .6, .3); // Background color green

      renderWindow->Render();
      renderWindowInteractor->Start();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 2.8)

    PROJECT(MatrixMathFilter)

    find_package(VTK REQUIRED)
    include(${VTK_USE_FILE})

    add_executable(MatrixMathFilter MACOSX_BUNDLE MatrixMathFilter.cxx )

    target_link_libraries(MatrixMathFilter ${VTK_LIBRARIES})

### Download and Build MatrixMathFilter

Click here to download MatrixMathFilter and its CMakeLists.txt file. Once the tarball MatrixMathFilter.tar has been downloaded and extracted,

    cd MatrixMathFilter/build

If VTK is installed:

    cmake ..

If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

    cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

    make

and run it:

    ./MatrixMathFilter

WINDOWS USERS PLEASE NOTE: Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.