粗糙集代数关系的图结构分析是粗糙集理论中又一研究方向。
The graphic structure analysis for algebraic relationship of rough sets is a new research direction of the rough set theory.
答案要看 simplex 算法背后采用的代数关系，但是有关它是如何工作的解释已经超出了本文的范围。
The answer is in the algebra behind the simplex algorithm, but explaining how it works is beyond the scope of this article.
也是一个关于此话题的很好的介绍，解释了ActiveRecord 3中的“关系代数”背后的的动机和理论。
Is also a great introduction to this topic and shows the motivation and theory behind the "relational algebra" in ActiveRecord 3.
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