很明显，你会看到一个，简谐振荡。
It's clear that you're going to see a simple harmonic oscillation.
我们知道初始条件，我们知道这是简谐振荡，我们想知道，最大位移是多少。
We know the initial conditions, and we know it's a simple harmonic oscillation, and we want to know what the maximum displacement is going to be.
以前算过-,这是能量守恒，为了算出,简谐振荡的周期，我们求时间导数。
We've done this before-- this is the conservation of energy, and in order to find the period of the simple harmonic oscillation, we take the time derivative.
能流密度不再随时间作简谐振荡，它的振幅构成一个高斯形状的包络。
The instantaneous energy density does not oscillate with time at the harmonic form, its amplitude forms and envelope with Gaussian shape.
能流密度不再随时间作简谐振荡，它的振幅构成一个高斯形状的包络。
The instantaneous energy density does not oscillate with time at the harmonic form, its amplitude forms and envelope with Gaussian shape.
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