# How to create a symbolic general (without explicit definition) function?

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Yunshen Huang el 10 de Mzo. de 2021
Comentada: Yunshen Huang el 14 de Mzo. de 2021
Hi all,
I want to know how to create a general function in symbolic way. My goal is to examine the differentials of the overall function in terms of a variable, where there are some functions of this variable that I am not interested in. I checked some documents, all ask me to explicitly define those functions.
Here is a example I am thinking of, which is realized in the psudo code:
syms x g real
f = x*g(x);
fdx = simplify(diff(f,x))
where g is the general function that I want to create. Therefore, this code is supposed to give me the result like:
fdx = g(x)+x*ddxg(x)
Since I really don't care the expression of g(x), a representation like ddxg(x) is what I want in the result.
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Prudhvi Peddagoni el 12 de Mzo. de 2021
Hi,
You need to specify that g is a function of x like this:
syms x g(x)
f = x*g;
fdx = diff(f,x);
Hope this helps.
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Yunshen Huang el 14 de Mzo. de 2021
Thanks! it works exactly as I want

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