为什么要说F是一个梯度场？
What is meant by social gradient?
社会梯度是什么？
Now it should be a gradient field.
那么它应该就是一个梯度场。
也就是梯度场。
What is the gradient of this function?
这个函数的梯度是什么？
This is the social gradient in health.
这就是健康方面的社会梯度。
它不是梯度。
So, indeed, this is not a gradient field.
因此这不是一个梯度场。
Well, you take the gradient of a function.
作出一个函数的梯度。
The normal vector will just be the gradient.
法向量就是梯度向量。
Well, so, what's the gradient of this function?
那么，这一函数的梯度是什么？
Yes? How do I know the direction of a gradient?
我怎样知道梯度的方向？
OK.So what is our test for gradient fields?
那么怎样验证有势场呢？
Find the gradient. Find an approximation formula.
求梯度和近似公式。
It is a gradient field. We need three conditions.
这是一个有势场，我们需要三个条件。
The problem is not every vector field is a gradient.
问题是，不是所有向量场都是梯度。
So, the way to do it is that we compute the gradient.
方法应该是去计算出梯度。
So how do we get a gradient background on a shell?
那么如何在shell上得到渐变的背景色呢？
But, so here's the first cool property of the gradient.
现在我们来看看梯度的第一个好性质。
The question is for which value of a is this a gradient?
问题是a取多少时，这是一个梯度场？
We have said if we have a gradient field then we have this.
如果有一个梯度场，那就能得到这个。
Well, the gradient is also a way to package partials together.
同样地，梯度也是把偏导数糅合到一起。
If you have a gradient field then it should have this property.
如果给定一个梯度场，那么它就应该满足这个性质。
Altitude measurements mean the road's gradient can be determined.
海拔测量还可以判定出道路的坡度。
Yes? How do you determine whether something is a gradient or not?
怎样确定一个场是不是梯度？
Click on the gradient to open up the gradient Editor dialog box.
点击渐变条打开渐变面板。
So, if actually show you the gradient, you can't really see it here.
如果展示梯度的话，在这儿是看不到的。
We have seen that the gradient is perpendicular to the level surface.
我们已经知道，梯度是垂直于等值面的。
Now we are going to create a sky gradient for the top of the canvas.
现在，我们要为画布顶端创建一个天空蓝色渐变。
Say that f, our vector field is actually the gradient of some function.
也就是向量场f实际上是一个函数的梯度。
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