借助于变量代换，求解几类线性微分方程，并得到了几个求解的充分必要条件。

With variable substitution, several kinds of linear differential equations are solved and several sufficient and necessary conditions are obtained.

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同时，引入变量代换，基于线性规划的单纯形法，提出该类绝对值规划问题的全局优化求解算法。

Based on variable substitution and the simplex method for linear programming, the paper also discusses the global optimization algorithm for the absolute value programming.

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给出了代换盒的非线性度与其分量组合函数线性结构之间的密切联系。

Also, we formulate the nonlinearity by linear structures of its nonzero combination functions.

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