I still don't know what eigenvalues are, what they're for, or how to use them, but I needed to calculate them for work and make sure they were positive.

I use MSVC at work and none of the other packages I looked at had VS solutions or projects. One did, but it didn't compile. I used the Eigen package and since it's templates based “compiling” is the simple part.

Download Eigen from: http://eigen.tuxfamily.org

```
#include <Eigen/Eigen>
using namespace Eigen;
void PrintEigenvalues( Array inputs )
{
MatrixXd matrix( inputs.GetSize(), inputs.GetSize() ); // rows, cols
// populate the matrix via inputs. matrix(r,c) = n;
SelfAdjointEigenSolver<MatrixXd> solver( matrix );
SelfAdjointEigenSolver<MatrixXd>::RealVectorType values = solver.eigenvalues();
cout << values << endl;
}
```

I never did figure out how to call matrix.eigenvalues(), kept getting “Flags&SelfAdjointBit” assertions.

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