Result of SelfAdjointEigenSolver saved as member is reinitialized when in another scope - c++

Question

I'm trying to run a pca on an block of an eigen matrix.
The observation in the input matrix are in columns.
I want to save the eigen vectors as a matrix for later use.
But the matrix (m_pcaCoefs) "gets reinitialized" when I use it in another scope, inside the class of course.
I'm pretty sure I'm missing something on how eigen works !
class foo {
public:
using InputMatrixType = Eigen::Matrix<double,Eigen::Dynamic,Eigen::Dynamic>;
void computePca(InputMatrixType & inputMatrix)
{
// m_pcaCoefs is a private member of dense matrix type
size_t start = 1;
auto r = inputMatrix.rows();
auto c = inputMatrix.cols();
Eigen::Block<InputMatrixType> inputBlock
= inputMatrix.block( start, 0 ,r-start , c );
// center the data
m_pixelValueMeans = inputBlock.rowwise().mean();
inputBlock.colwise() -= m_pixelValueMeans;
// inputBlock is a d by n, where d is the number of observation
InputMatrixType cov = inputBlock * inputBlock.adjoint();
cov = cov / (c - 1);
Eigen::SelfAdjointEigenSolver<InputMatrixType> eig(cov);
InputMatrixType m_pcaCoefs = eig.eigenvectors();
// here m_pcaCoefs looks fine
std::cout << m_pcaCoefs.size() << std::endl; // output: 9
}
void print()
{
std::cout << m_pcaCoefs.size() << std::endl; // output: 0
}
protected:
InputMatrixType m_pcaCoefs;
}
int main()
{
foo test;
test.computePca(someMatrix); // outputs 9
test.print() // output 0
}
Any clue how to get the eigenvectors to be copied to m_pcaCoefs ?

Answer 1

InputMatrixType m_pcaCoefs = eig.eigenvectors();
this is not what you're thinking which is a member of your class.
you should just use:
m_pcaCoefs = eig.eigenvectors(); // use member m_pcaCoefs