How to get correct partial derivatives using diff function?

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Robert Flores 2019-10-1

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https://ww2.mathworks.cn/matlabcentral/answers/482941-how-to-get-correct-partial-derivatives-using-diff-function

评论： Robert Flores 2019-10-1

Hello,

I am trying to take the derivative of a logorithum that consists of three varibles, x1, x2, and u. I think the syntax of my code works somewhat okay, because I get part of the solution. However, I know it is wrong because I did it by hand, and I am missing some terms in the MatLab output. Below is a copy of my code so far. If anyone can help me resolve this issue, it will be greatly appreciated, thank you in advance.

I have attached a image of what the solution should look like.

Sincerely,

Robert

CODE:

clc, clear, close all 
syms x1 x2 u 
J = log(x1)+2*log(x2)+3*log(u);
% J = combine(J,'log','IgnoreAnalyticConstraints',true);
delJdelx1 = diff(J,x1)
delJdelx2 = diff(J,x2)