how to rewrite an equation in terms of another equation?

Hi. I have an equation for example like this:

sigma = 4*q*y^3/(b*h^3)

and I introduce that:

I = b*h^3/12

now I want to know how can I rewrite "sigma" in terms of "I"?

[pfb]

Looks like the denominator in parentheses in sigma is 12 times I.

But how is this a matlab question?

[Omidreza Ghafarinejad]

The question is very simple. I want to rewrite sigma in terms of I. I don't want to do it by hand. I want matlab to do this job for me. Consider that the sigma here is just an example. I have 3 equations that are longer than sigma here.Calculating all of them in terms of "I" takes so much time so I want matlab to do it for me. For example it should show me the sigma like this:

sigma = q*y^3/3*I

[pfb]

Ok, now that you have explained it, I understand. Perhaps I'm a bit slow.

Anyway, duplicating the question in the "tags" field is not very helpful.

Referring to symbolic calculations would have been more helpful.

Answer 1

[Star Strider]

This works:

syms q y b h I
sigma = 4*q*y^3/(b*h^3);
Eq1 = I == b*h^3/12;
b = solve(Eq1,b);
sigma = subs(sigma)

produces:

sigma =

(q*y^3)/(3*I)

[Omidreza Ghafarinejad]

thanks. it worked

[Star Strider]

My pleasure.