Function inv_cond

dependence/eigen-3.4.0/doc/examples/function_taking_ref.cpp:6–10

using namespace std;

float inv_cond(const Ref<const MatrixXf>& a)
{
  const VectorXf sing_vals = a.jacobiSvd().singularValues();
  return sing_vals(sing_vals.size()-1) / sing_vals(0);
}

int main()
{