EigenSymmetric
VTKExamples/Cxx/Math/EigenSymmetric
Description¶
At the moment, this is a pretty messy process, so here are some helper functions that will hopefully eventually be wrapped into a class/interface.
Code¶
EigenSymmetric.cxx
#include <vtkMath.h> /* allocate memory for an nrow x ncol matrix */ template<class TReal> TReal **create_matrix ( long nrow, long ncol ) { typedef TReal* TRealPointer; TReal **m = new TRealPointer[nrow]; TReal* block = ( TReal* ) calloc ( nrow*ncol, sizeof ( TReal ) ); m[0] = block; for ( int row = 1; row < nrow; ++row ) { m[ row ] = &block[ row * ncol ]; } return m; } /* free a TReal matrix allocated with matrix() */ template<class TReal> void free_matrix ( TReal **m ) { free ( m[0] ); delete[] m; } int main(int, char *[]) { // Create this matrix // 1 2 3 // 2 5 9 // 3 9 8 double **a = create_matrix<double> ( 3,3 ); a[0][0] = 1; a[0][1] = 2; a[0][2] = 3; a[1][0] = 2; a[1][1] = 5; a[1][2] = 9; a[2][0] = 3; a[2][1] = 9; a[2][2] = 8; //create a matrix for the eigenvectors to be stored in double **w = create_matrix<double> ( 3,3 ); //create a vector for the eigenvalues to be stored in double v[3]; //compute the eigenvalues/vectors vtkMath::Jacobi ( a,v,w ); //output eigen values std::cout << "Eigen values (decreasing order): " << std::endl; for ( int i=0; i<3; i++ ) { std::cout << v[i] << " "; } //output eigenvectors std::cout << "Eigen vectors (same order as eigen values): " << std::endl; for ( int i=0; i<3; i++ ) { //the columns of w are the eigenvectors std::cout << "Eigen vector " << i << " : " << w[0][i] << " " << w[1][i] << " " << w[2][i] << std::endl; } //clean up free_matrix ( w ); free_matrix ( a ); return EXIT_SUCCESS; }
CMakeLists.txt¶
cmake_minimum_required(VERSION 2.8) PROJECT(EigenSymmetric) find_package(VTK REQUIRED) include(${VTK_USE_FILE}) add_executable(EigenSymmetric MACOSX_BUNDLE EigenSymmetric.cxx) target_link_libraries(EigenSymmetric ${VTK_LIBRARIES})
Download and Build EigenSymmetric¶
Danger
The generation of tar files has not been ported to the new VTKExamples. Some tarballs may be missing or out-of-date.
Click here to download EigenSymmetric and its CMakeLists.txt file. Once the tarball EigenSymmetric.tar has been downloaded and extracted,
cd EigenSymmetric/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:
./EigenSymmetric
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.