fix test with eigen
On "some" PCs, most notably my desktop the test of MARQOV with eigen fails. I found out that this due to an incorrect use of the {} syntax for initialization. StateVector{0} is a constructor call. In the case of Eigen this leads to the creation of a vector of a specified size with 0. StateVector{} is initialization, which for aggregate types(e.g. structs, arrays) performs zero initialization. The last is also the behaviour that we intended to be used.