second-order equation meaning in English

二阶方程

By using a fixed point theorem in cones , we investigate a second - order equation and the theorem of existence of unique positive periodic solution is given
摘要应用不动点定理，研究了一类二阶时滞微分方程，给出了其唯一周期正解的存在性定理。
After an error analysis is made in detail for second - order equations and some essential points of genetic algorithm in fault diagnosis are also illustrated , an improved genetic algorithm is adopted to choose an optimal test frequency
本文对二阶灵敏度故障诊断方程进行了详尽的误差分析,同时在详细阐述了故障诊断应用中的遗传算法操作要点后,使用改进遗传算法来选择优化的测试频率。