Asked by Oscarin
on 5 Sep 2018 at 21:43

Hello I have a problem, I tryed to derive a equation like "a1^2*a2^2" but I got "ans = 2*a1*a2^2", This result is correct but If we take as variable only "a1" but I need to take as varible "a1" and "a2". I want to get this becase is a multiplication:

I have used diff () this is my code:

what is the correct way to say matlab which are my variables?

Thank you very much I wait for your answer.

Answer by D_coder
on 15 Sep 2018 at 22:53

Edited by D_coder
on 15 Sep 2018 at 22:53

You can try this

a = a1^2*a2^2; diff(a,a1) + diff(a,a2);

ans =

2*a1^2*a2 + 2*a1*a2^2

Oscarin
on 15 Sep 2018 at 23:27

thaks for your answer but this is more difficult because I am developing a graphic interphase and I export the data and I need to derivate de ecuation but I need to derive with a lot of variable I show a example:

In this case the last Graphic Interphase exported the data and I need to derive with variables "d1", "d2" and "t1". That's difficult because the ecuation it's different each time.

I have a list of possible variables but not all of them always appear because some of them based on the analysis become 0

Thanks

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Answer by Walter Roberson
on 15 Sep 2018 at 23:43

You can use gradient() to find the diff(), and you could sum() the result.

Walter Roberson
on 19 Sep 2018 at 1:06

You can use pretty(), or you can use LiveScript .

Oscarin
on 20 Sep 2018 at 1:03

I try to use pretty () but matlab show a error.

but this is the problema I fill in with this ecuation.

I want to get the first ecuation on next picture. But If it were possible to obtain it with the notation of the second equation, it would be better

Walter Roberson
on 20 Sep 2018 at 2:10

BL = latex(B)

But then you would have to display the latex stored in BL somehow.

You **cannot** get the graphical format you want to store into a variable. That format is a graphical format that is not how MATLAB represents symbolic expressions internally. You can render into latex like I show, but the result is a character vector that cannot be operated on symbolically.

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