cpp_wrapper_irving_check_stability: Check if a matching solves the stable roommate problem
In matchingR: Matching Algorithms in R and C++

This function checks if a given matching is stable for a particular set of preferences. This function checks if there's an unmatched pair that would rather be matched with each other than with their assigned partners.

1	cpp_wrapper_irving_check_stability(pref, matchings)

`pref`	is a matrix with the preference order of each individual in the market. If there are `n` individuals, then this matrix will be of dimension `n-1` by `n`. The `i,j`th element refers to `j`'s `i`th most favorite partner. Preference orders must be specified using C++ indexing (starting at 0). The matrix `pref` must be of dimension `n-1` by `n`.
`matchings`	is a vector of length `n` corresponding to the matchings that were formed (using C++ indexing). E.g. if the `4`th element of this vector is `0` then individual `4` was matched with individual `1`. If no stable matching exists, then this function returns a vector of zeros.