How to differentiate several symbolic functions?

I have 3 symbolic functions; L10(a) , L1(u,a) and finally epsilon1(u). I wish to differentiate the last symbolic function (epsilon1) with respect to u, but it only gives me 0 because it does not take into account how I defined L1 and L10 previously which contains u. How can I solve this?

syms L10(a) 
L10(a) = 2*a;

syms L1(u,a)
L1(u,a) = sqrt((2*a)^2+u^2);

syms epsilon1(L1,L10)
epsilon1(u) = (L1-L10)/L10;

df = diff(epsilon1(u),u)

Answer 1

[madhan ravi]

syms L10(a) L1(a,u) epsilon1(a,u)
L10(a) = 2*a;
L1(a,u) = sqrt((2*a)^2+u^2);
epsilon1(a,u) = (L1(a,u)-L10(a))/L10(a);
df = diff(epsilon1(a,u),u)

[Ruslan Khoguev]

Thank you

[Ruslan Khoguev]

Does this code look correct to you? I get a long answer and I am unable to confirm if its right or not.

syms L10(a) L1(a,u) epsilon1(a,u) L20(a) N1(a,u,EA) N2(a,u,EA) P(a,u,EA)

L10(a) = 2*a;

L20(a) = sqrt(5)*a;

L1(a,u) = sqrt((2*a)^2+u^2);

L2(a,u) = sqrt((2*a)^2+(a-u)^2);

epsilon1(a,u) = (L1(a,u)-L10(a))/L10(a);

epsilon2(a,u) = (L2(a,u)-L20(a))/L20(a);

N1(a,u) = EA*epsilon1;

N2(a,u) = EA*epsilon2;

P(a,u,EA) = (u/L1)*N1-((a*u)/L2)*N2

df = diff(P(a,u,EA),u)