So the first thing is, let's approximate that we could take the sum not to some finite level, which would be the case if there's a finite number of elements in the chain.

那么第一件事，让我们估算它们的和，不是对有限能级求和，有限能级适用于，分子链中有有限数目的结构单元的情况。

The transformation of Gaussian beams is taken as an example, an approximate analytical propagation expression in terms of a sum of elementary functions is derived.

以高斯光束的变换为例，推导出了一个表示为初等函数之和的近似解析传输公式。

With the rectangular function expanded into a finite sum of complex Gaussian functions, an approximate analytical propagation equation of HChG beams is derived.

采用将矩形函数展开为有限个复高斯函数之和的方法，推导出了光场分布的解析表达式。

But I would like to know the approximate sum so that I may cash traveller's check.

请告诉我付费的大概数字,我好兑换现款.大约五百元. 包括服务费吗?一切都包括在内了.