# How do i define a variable as a function?

조회 수: 2(최근 30일)
Hamza Yusuf 2021년 10월 11일
댓글: Star Strider 2021년 10월 11일
Let us say there is a fucntion theta that is depedent on time: Theta(t); It is in a cos function so: cos(theta(t))
How do i differentiate this in matlab so it uses the chain rule?
clear all
syms t theta
theta=t;
f=cos(theta(t));
diff(f,t)
I have tried the above and got the errors:
Error using sym/subsref (line 49)
Error using maplemex
Error, (in MTM:-subsref) indices must be positive integers, got t
Error in test (line 5)
f=cos(theta(t));

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### 채택된 답변

Star Strider 2021년 10월 11일
I suspect this works the similiarly in Maple (that I do not currently have) —
syms t theta(t)
f=cos(theta(t));
dfdt(t) = diff(f,t)
dfdt(t) = .
##### 댓글 수: 7표시숨기기 이전 댓글 수: 6
Star Strider 2021년 10월 11일
I hope that you do not have to uninstall Maple, and can simply disconnect it from MATLAB.
However if you need to uninstall it (and then reinstall it without connecting it to MATLAB next time), and since it appears that you are using Windows, open Control Panel, then click on Programs and Features, then follow the instructions. Then, reinstall Maple without connecting it to MATLAB.
.

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### 추가 답변(1개)

KSSV 2021년 10월 11일
syms theta(t)
f=cos(theta(t));
diff(f,t)
##### 댓글 수: 1표시숨기기 없음
Hamza Yusuf 2021년 10월 11일
I get this error:
Error using assignin
Invalid variable name "theta(t)" in ASSIGNIN.
Error in syms (line 47)
assignin('caller',varargin{1},sym(varargin{1}));
Error in test (line 1)
syms theta(t)

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R2020b

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