This enumeration lists the values that tell for which type of
solution the incumbent callback or lazy constraint callback was invoked.
NodeSolution
The integral solution was found as the solution to an LP-relaxation
of a node in the search tree.
HeuristicSolution
The integral solution was found by a CPLEX internal heuristic.
UserSolution
The integral solution was found by the user's heuristic callback function.
This value is returned only in incumbent callbacks, not in lazy constraint
callbacks.
MIPStartSolution
The integral solution was found during MIP start processing.
Note that callbacks invoked in this situation do not have the full API
available. For example, you cannot set/get user data to a node, nor can
you do anything else that requires a search tree node context.
