Just know that the optimal solution for a non-integer problem is always one of the polyhedron vertices.
我们只需要知道非整型问题的优化解决方案通常都是一个多面体的顶点就好了。
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In other words, the feasible region is not a polyhedron; it's composed only of the integer (x1, x2,..., xn) pairs inside or at the boundaries of the actual polyhedron of the relaxed problem.