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
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.