Implement ULX crossover

[abeham]

This crossover is described in Tate, D. M. & Smith, A. E. A genetic approach to the quadratic assignment problem Computers & Operations Research, 1995, 22, 73-83.

[abeham]

r6056

• Added the ULX crossover for permutation encodings
• Added an IEqualityComparer<Permutation> that will check whether two permutations are equal

[abeham]

r6342

• merged to trunk

[mkommend]

PermutationEqualityComparer

• GetHashCode(Permutation obj) should follow the same logic as the comparison for equality
• should derive from EqualityComparer<Permutation> instead of implementing IEqualityComparer<Permutation>
• EqualsAbsolute(Permutation x, Permutation y) could be written as return x.SequenceEquals(y);

UniformLikeCrossOver

• I would write the overriden Cross method before the static implementation to have a more natural reading flow.
• IMHO it is reasonable to seal the class as subclassing makes no sense. What do you think of this?

The remaining source code looks very good.

[abeham]

r6507

• Made ULX crossover sealed
• PermutationEqualityComparer
  • Now derives from EqualityComparer<Permutation>
  • Fixed the GetHashCode function to return the same hash value when the objects are equal according to the equals function. The function is probably not that efficient using string's GetHashCode, but I couldn't come up with an easier solution in time.
  • Created a unit test to test this comparer

Thanks for reviewing, the Cross method is below the static implementation in most other crossovers and manipulation operators as well.

[mkommend]

r6512: Corrected access modifiers of the cloning and storable ctor.