ILOG CPLEX .NET Reference Manual

Cplex.SolveCallback.IsDualFeasible Method 

Returns true if a dual feasible solution is available for the current node.

public virtual bool IsDualFeasible();

Remarks

If false is returned, the solution may still be dual feasible, but the algorithm has not determined the feasibility before it terminated.

See Also

Cplex.SolveCallback Class | ILOG.CPLEX Namespace