MATLAB Answers

Symbolic Subs Function isn't picking up formula

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Mauricio Medaets
Mauricio Medaets on 24 May 2020
Answered: Sai Sri Pathuri on 27 May 2020
This is pretty strightforward:
I define a generic symbolic function, say theta(t), then later in the code I want to define the actual formula of theta(t) being, let's say, t^2.
And I need a means of substituting (or "updating") wherever I referenced theta(t) with t^2, which I assume the subs function is designed for and should do automatically.
Please let me know what am I missing or what other function to use.
Thanks
syms t theta(t)
a(t) = t*theta(t)
theta(t) = t^2
subs(a)
% which gives me:
ans(t) = t*theta(t) % BUT IT SHOULD BE t^3 !!!

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Answers (1)

Sai Sri Pathuri
Sai Sri Pathuri on 27 May 2020
In your code, both a and thetha are functions of t. When you use subs function, the value of t will be substituted. Hence you are getting the above answer. You may use following code to obtain desired answer
syms t theta
a(t) = t*theta
theta = t^2
subs(a)

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