Selecting part of an equation

[ianchlee]

I have an equation written as eq = TexMobject(r"\frac {x_1 x_2}{x_1 + x_2}"). I want to select x_1 for some manipulation. In particular, I want to color it without changing the other texts, and animate equation transformation, by moving x_1 into its place at eq2 = TexMobject(r"\frac{1}{x_1} + \frac{1}{x_2}"). Could someone point me some directions on how to solve this? Many thanks!

[TonyCrane]

In your code, x_1 in eq is eq[0][:2], and in eq2 is eq2[0][2:4]. The whole index-mob maps in eq and eq2 are:


So you can try:

self.play(TransformFromCopy(eq[0][:2], eq2[0][2:4]))

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btw, if you want to learn more about TexMobject and it’s structure in manim, you can watch this video. (Although this video is in Chinese, it has no great influence on learning the content. You can just watch the screen and ignore the Chinese subtitles.)

[ianchlee]

Thanks! This helped a lot!

[3b1b]

The other way to do this would be to wrap the parts you want to be separated with two curly braces. It's slightly awkward with fractions, since this functionality depends on the ordering of the parts of the string defining your Tex to match the ordering of symbols, so instead of using \frac{}{} you need to use \over.

eq = Tex(r"{ {{x_1}} {{x_2}} \over {{x_1}}+{{x_2}}}")

You could also write

eq = Tex(r"x_1 x_2 \over x_1 + x_2", isolate=["x_1", "x_2"])

Once it's been initialized like this, you can call things like eq.get_parts_by_tex("x_1") or eq.set_color_by_tex("x_1", BLUE)