Hi,
In some lapack functions there is an output parameter called "info" which return if there is or not a illegal coefficient or if a factorisation occured successfully. Is there the same king of thing in Eigen for example for the QR factorisation?

There should be an info() method that returns wether the decomposition / solving was a Success, or if some NumericalIssue appears, etc. Check the documentation of this method for details.