For periodic waveforms, the Fourier series representations are valid over all time.

对于周期波形，傅立叶级数表示法在整个时间段都是有效的。

Rayleigh reflectance can be approximated using Fourier series relevant to angles and wavelength.

其中，瑞利反射率可以用与角度和波长有关的傅立叶级数近似。

Such series (e. g., the Fourier series) are particularly useful in solving differential equations.

有的级数(如傅立叶级数)用来解微分方程序特别有用。

The Fourier transform is an integral expression for a Fourier series applied to an infinitely long signal.

作为这种方法的一个例子，让我们计算一个方波的傅里叶级数。

A periodic function, finite Fourier series, is used to activate the actuator for obtaining training samples.

用周期函数，有限项傅立叶级数，作为激励函数来获取训练样本。