Symbolic Subs Function isn't picking up formula

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 !!!

Answer 1

[Sai Sri Pathuri]

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)