Extracting only real parameter values using 'lsqcurvefit' or 'fminsearch'

Hi, I am trying to fit the impedance of a circuit model to one generated from experiment. I can define the circuit model consisting of R,L,C. From the fitted impedance curves, I then want to extract the parameter values of R,L,C. My problem is the values generated are complex numbers. I want only real R,L, C values to be generated. Any suggestions?

I tried writing a code like this:

x0 = [Rm Lm Cm C_0 Rc Cc];

opts = optimset('Algorithm', 'levenberg-marquardt','Display', 'off','MaxIter',1e5, 'DiffMinChange', 1e-10, 'MaxFunEvals',1e5,'TolFun',1E-20,'TolX',1E-10); [ n, resnorm, residual, exitflag] = lsqcurvefit(@fun_complex,x0,w,ydata,[],[],opts);

where, function reZ = fun_complex(x,w)

% Rx = x(1); % Lx = x(2); % Cx = x(3); % C0 = x(4); x2 = x(2)/1e6; x3 = x(3)/1e12; x4 = x(4)/1e12;

Zmb = x(1) + j.*w.*x2+ 1./(j*w*x3); Zelec = 1./(j*w*x4);

Ymb = 1./Zmb; Yelec = 1./Zelec; Yx = Ymb + Yelec;

Z = 1./Yx;

reZ = Z; end