Dot indexing is not supported for variables of this type.

When I am running my code, I get a response that a built-in with syms is not running correctly.

syms F D l t w

% Stress

n_stress = F./(t.*w);
u_nstress = sqrt((diff(n_stress,F).*u_f).^2+(diff(n_stress,t).u_c).^2+(diff(n_stress,w).*u_c).^2)

Unrecognized function or variable 'u_f'.

Dot indexing is not supported for variables of this type. 

Error in sym/subsref (line 909)
            R_tilde = builtin('subsref',L_tilde,Idx);
            
Error in Carbon90 (line 29)

[Ryan]

u_f and other functions are defined above I just did not include them.

Answer 1

[Image Analyst]

diff(n_stress,t) is a vector. It does not have a u_c field. Perhaps you meant

diff(n_stress,t) .* u_c