Problem with optimizing a function which has indirect variables (variables are a set of data that is generated with the help of another function)

I desperately need to find a way to solve this for my work ,

 i have a certain function which calculates the fit of my chosen parameters, i have to find the parameters which gives the min possible fit value

above is the fit function R(Tn) and I(Tn) is the true data Rn^(k) and In^(k) are the variables .

Rn^(k) and In^(k) are generated from another function which is as follows

if true
 function [Z, phase] = modelMT(resistivities, thicknesses,frequency)
% code
end
Rn^(k) - real(Z);
In^(k) - imag(Z);

it takes set of resistivities and thicknesses , i need to choose these values for which i get the min of fit function .

[Walter Roberson]

duplicates http://uk.mathworks.com/matlabcentral/answers/223986-problem-with-optimizing-a-function-which-has-indirect-variables-variables-are-a-set-of-data-that-is