# VTK/Examples/Cxx/Math/HomogeneousLeastSquares

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## HomogeneousLeastSquares.cxx

```#include <vtkSmartPointer.h>
#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 = 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 );
delete[] m;
}

int main (int, char *[])
{

//Solve XM = Y;

int numberOfSamples = 3;
int numberOfVariables = 2;
double **x = create_matrix<double> (numberOfSamples, numberOfVariables);
x = 1; x = 2;
x = 2; x = 4;
x = 3; x = 6;

double **m = create_matrix<double> ( numberOfVariables, 1 );

vtkMath::SolveHomogeneousLeastSquares(numberOfSamples, x, numberOfVariables, m);

std::cout << "Solution is: " << m << " " << m << std::endl;

free_matrix(x);
free_matrix(m);

return EXIT_SUCCESS;
}
```

# Please try the new VTKExamples website.

## CMakeLists.txt

```cmake_minimum_required(VERSION 2.8)

PROJECT(HomogeneousLeastSquares)

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

add_executable(HomogeneousLeastSquares MACOSX_BUNDLE HomogeneousLeastSquares.cxx)

if(VTK_LIBRARIES)
target_link_libraries(HomogeneousLeastSquares \${VTK_LIBRARIES})
else()
target_link_libraries(HomogeneousLeastSquares vtkHybrid vtkWidgets)
endif()
```

## Download and Build HomogeneousLeastSquares

Click here to download HomogeneousLeastSquares. and its CMakeLists.txt file.

Once the tarball HomogeneousLeastSquares.tar has been downloaded and extracted,

```cd HomogeneousLeastSquares/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:

```./HomogeneousLeastSquares
```

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.