# MinimumSpanningTree

VTKExamples/Cxx/Graphs/MinimumSpanningTree

### Description

This example shows how to find the minimum spanning tree. The input graph is:

and the minimum spanning tree computed is :

You must have compiled VTK with VTK_USE_BOOST=ON to use this functionality. You must also link to vtkInfovis.

### Code

MinimumSpanningTree.cxx

    #include <vtkSmartPointer.h>

    #include <vtkBoostPrimMinimumSpanningTree.h>
    #include <vtkDataSetAttributes.h>
    #include <vtkDoubleArray.h>
    #include <vtkMutableUndirectedGraph.h>
    #include <vtkTree.h>

    int main(int, char *[])
    {
      vtkSmartPointer<vtkMutableUndirectedGraph> g =
        vtkSmartPointer<vtkMutableUndirectedGraph>::New();

      // Create 3 vertices
      vtkIdType v1 = g->AddVertex();
      vtkIdType v2 = g->AddVertex();
      vtkIdType v3 = g->AddVertex();

      // Create a fully connected graph
      g->AddEdge(v1, v2);
      g->AddEdge(v2, v3);
      g->AddEdge(v1, v3);

      // Create the edge weight array
      vtkSmartPointer<vtkDoubleArray> weights =
        vtkSmartPointer<vtkDoubleArray>::New();
      weights->SetNumberOfComponents(1);
      weights->SetName("Weights");

      // Set the edge weights
      weights->InsertNextValue(1.0);
      weights->InsertNextValue(1.0);
      weights->InsertNextValue(2.0);

      // Add the edge weight array to the graph
      g->GetEdgeData()->AddArray(weights);

      // Output original graph info
      std::cout << "Number of vertices: "
                << g->GetNumberOfVertices() << std::endl;
      std::cout << "Number of edges: "
                << g->GetNumberOfEdges() << std::endl;
      g->Dump();

      // Setup the minimum spanning tree filter
      vtkSmartPointer<vtkBoostPrimMinimumSpanningTree> minimumSpanningTreeFilter =
        vtkSmartPointer<vtkBoostPrimMinimumSpanningTree>::New();
      minimumSpanningTreeFilter->SetOriginVertex(v1);
      minimumSpanningTreeFilter->SetInput(g);
      minimumSpanningTreeFilter->SetEdgeWeightArrayName("Weights");

      // Compute the minimum spanning tree
      minimumSpanningTreeFilter->Update();

      // Get the output tree
      vtkSmartPointer<vtkTree> minimumSpanningTree = vtkSmartPointer<vtkTree>::New();
      minimumSpanningTree->ShallowCopy(minimumSpanningTreeFilter->GetOutput());

      // Output information about the minimum spanning tree
      std::cout << "Number of vertices: "
                << minimumSpanningTree->GetNumberOfVertices() << std::endl;
      std::cout << "Number of edges: "
                << minimumSpanningTree->GetNumberOfEdges() << std::endl;
      minimumSpanningTree->Dump();

      return EXIT_SUCCESS;
    }

### CMakeLists.txt

    cmake_minimum_required(VERSION 3.3 FATAL_ERROR)

    project(MinimumSpanningTree)

    find_package(VTK COMPONENTS
      vtkCommonCore
      vtkCommonDataModel
      vtkInfovisBoostGraphAlgorithms QUIET)
    if (NOT VTK_FOUND)
      message("Skipping MinimumSpanningTree: ${VTK_NOT_FOUND_MESSAGE}")
      return ()
    endif()
    message (STATUS "VTK_VERSION: ${VTK_VERSION}")
    if (VTK_VERSION VERSION_LESS "8.90.0")
      # old system
      include(${VTK_USE_FILE})
      add_executable(MinimumSpanningTree MACOSX_BUNDLE MinimumSpanningTree.cxx )
      target_link_libraries(MinimumSpanningTree PRIVATE ${VTK_LIBRARIES})
    else ()
      # include all components
      add_executable(MinimumSpanningTree MACOSX_BUNDLE MinimumSpanningTree.cxx )
      target_link_libraries(MinimumSpanningTree PRIVATE ${VTK_LIBRARIES})
      # vtk_module_autoinit is needed
      vtk_module_autoinit(
        TARGETS MinimumSpanningTree
        MODULES ${VTK_LIBRARIES}
        )
    endif ()

### Download and Build MinimumSpanningTree

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

    cd MinimumSpanningTree/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:

    ./MinimumSpanningTree

WINDOWS USERS

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