Checker functions for min cost flow

[Peter Kovacs]

Maybe we could have checker functions for the minimum cost flow algorithms according to the test file. E.g. checkFeasibility() and checkOptimality() or checkFlow() and checkPotential(). They would be similar to the checker functions of Circulation.

However it is questionable whether these functions should be introduced to all MCF algorithms or we should have them separetly, since the implementation would be independent form the algorithms.

[Peter Kovacs]

I suggest separate checker functons/classes for each problem for which we (will) have several solution methods, e.g. maximum flow, minimum cost flow etc.