From the theory and examples, the article points out why in the symmetric block the calculation of the double integral is easy to go wrong and offers some methods to avoid errors.
从理论和实例两个方面，指出了对称区域上二重积分计算中易出现问题的原因，并给出了避免错误的方法。
In statistical physics lectures, the calculation of the configuration partition function of molecule is simplified from double vectors integral to single vector integral.
统计物理教材中分子构型配分函数的计算，一般是将双矢量积分化简为单矢量积分。
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