取一个向量场的散度。
如果说函数的梯度是向量，那么向量场的散度就是函数。
So, if the gradient of a function is a vector, the divergence of a vector field is a function.
散度定理为我们提供了一种，计算向量场通过闭曲面的通量的方法。
So, the divergence theorem gives us a way to compute the flux of a vector field for a closed surface.
向量场，的散度，这两个定理说了什么呢？
Remember, the divergence of a vector field What do these two theorems say?
如果取一个有旋的向量场，流体流动方向是环绕某个坐标轴的，那么就会发现它的散度是零。
And, if you take a vector field where maybe everything is rotating, a flow that's just rotating about some axis, then you'll find that its divergence is zero.
如果取的向量场是处处恒定的，所有点都是平移关系，所以没有散度，因为导数为零。
If you take a vector field that is a constant vector field where everything just translates then there is no divergence involved because the derivatives will be zero.
如果取的向量场是处处恒定的，所有点都是平移关系，所以没有散度，因为导数为零。
If you take a vector field that is a constant vector field where everything just translates then there is no divergence involved because the derivatives will be zero.
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