UnboundLocalError: local variable 'R' referenced before assignment

[FabianPascher]

I use the R-RQ-RQ Fit Function [cir_RsRQRQ()] with

fit_params=Parameters()
fit_params.add('Rs', value=190, min=200, max=2000)
fit_params.add('R', value=150, min=100, max=4000)
fit_params.add('Q', value=10**-5, min=10**-7, max=10**-3)
fit_params.add('n', value=.8, min=.5, max=1)
fit_params.add('fs', value=10**-4, min=10**-6, max=10**-3)
fit_params.add('R2', value=2500, min=1000, max=4000)
fit_params.add('Q2', value=10**-4, min=10**-6, max=10**-3)
fit_params.add('n2', value=.8, min=.7, max=1)
fit_params.add('fs2', value=10**-5, min=10**-7, max=10**-3)

What I receive is:

Traceback (most recent call last):
File "C:\Users------------.py", line 73, in
Lennard_HIAT_C_2_5DC_80.EIS_fit(circuit='R-RQ-RQ', params=fit_params, weight_func='modulus')
File "C:\Users\fab54611\Anaconda3\lib\site-packages\PyEIS\PyEIS.py", line 4028, in EIS_fit
self.Fit.append(minimize(leastsq_errorfunc, params, method='leastsq', args=(self.df[i].w.values, self.df[i].re.values, self.df[i].im.values, circuit, weight_func), nan_policy=nan_policy, maxfev=9999990))
File "C:\Users--\Anaconda3\lib\site-packages\lmfit\minimizer.py", line 2583, in minimize
return fitter.minimize(method=method)
File "C:\Users--\Anaconda3\lib\site-packages\lmfit\minimizer.py", line 2352, in minimize
return function(**kwargs)
File "C:\Users--\Anaconda3\lib\site-packages\lmfit\minimizer.py", line 1689, in leastsq
lsout = scipy_leastsq(self.__residual, variables, **lskws)
File "C:\Users--\Anaconda3\lib\site-packages\scipy\optimize\minpack.py", line 410, in leastsq
shape, dtype = _check_func('leastsq', 'func', func, x0, args, n)
File "C:\Users--\Anaconda3\lib\site-packages\scipy\optimize\minpack.py", line 24, in _check_func
res = atleast_1d(thefunc(((x0[:numinputs],) + args)))
File "C:\Users--\Anaconda3\lib\site-packages\lmfit\minimizer.py", line 587, in __residual
out = self.userfcn(params, self.userargs, **self.userkws)
File "C:\Users--\Anaconda3\lib\site-packages\PyEIS\PyEIS.py", line 2128, in leastsq_errorfunc
re_fit = cir_RsRQRQ_fit(params, w).real
File "C:\Users--\Anaconda3\lib\site-packages\PyEIS\PyEIS.py", line 1249, in cir_RsRQRQ_fit
return Rs + (R/(1+RQ(w1j)**n)) + (R2/(1+R2Q2*(w*1j)**n2))
UnboundLocalError: local variable 'R' referenced before assignment

How to fix this?

[FabianPascher]

The solution is pretty easy. I made the mistake, that I defined the summit frequencies fs as well as the constant phase elements Q. This resulted in an overdetermined system. For my case, it makes sense to leave the Q and Q2 parameters out.
In general, you have to use three of the parameters in systems that contain R, Q, n and fs.
For more details, see the Equivalent Circuit Fitting Chapter in the very well written kbknudsen/PyEIS/blob/master/Tutorials/PyEIS_simulation_tutorial.ipynb
Thanks a lot for the library!