Freeing Eigen structures/variables

Hi @Erkaman 

Some structures from `Eigen` source are used.
```
typedef Eigen::SparseMatrix<double> SpMat;
typedef Eigen::Triplet<double> Triplet;
typedef Eigen::VectorXd Vec;

Eigen::SimplicialCholesky<SpMat> solver;
..
Vec solutionChannels[3];		
Vec b(numUnknowns);
```

How to free the memory used by Eigen entities ?