Error when use call function with undefined function '....' for input arguments of type 'double'

% Locate the operating point of PV module and

% calculate its voltage, current, and power

f = @(x) x - Rin*bp_sx150s(x,G,TaC);

Va_k = fzero (f, [0, 45]);

Ia_k = bp_sx150s(Va_k,G,TaC);

Pa_k = Va_k * Ia_k;

Error :

Anonymous functions are not supported for code generation

Undefined fucntionor variable 'z'

Undefined function or variable 'Va'

Anyone can advice?

Thx.