Updated m(RQ)-fit method implementation

CHANGELOG.md

@@ -32,6 +32,7 @@
 - Updated the `Warburg` element class to include an `n` exponent (fixed at 0.5 by default).
 - Updated the `plot_gamma` function to include a horizontal line marking zero on the y-axis.
 - Updated the automatic adjustment of initial values of circuit parameters to be bypassed when a non-default value is detected in a `Circuit` that is provided to the m(RQ)-fit method without a corresponding `FitResult`.
+- Updated the m(RQ)-fit method to support resistive-inductive `(RQ)` elements. The `n` parameter of the `ConstantPhaseElement` instance would then need to be `-1.0 <= n < 0.0`.
 - Fixed a bug that caused methods such as `DRTResult.get_peaks` to miss peaks at the time constant extremes.
 - Fixed a bug that caused an element's parameters in `FitResult.to_parameters_dataframe` to not be in a sorted order.
 - Fixed the previously unimplemented `FitResult.get_parameters` method.

src/pyimpspec/analysis/drt/mrq_fit.py

@@ -426,8 +426,11 @@ def _calculate_tau_gamma(
 
         n: float = parameters.get("n", 1.0)
         tau_0: float = (R * Y) ** (1.0 / n)
-        if isclose(n, 1.0, atol=1e-2):
-            gamma += R / (W * sqrt(pi)) * exp(-((ln(tau / tau_0) / W) ** 2))
+        if isclose(abs(n), 1.0, atol=1e-2):
+            gamma += (
+                R / (W * sqrt(pi)) * exp(-((ln(tau / tau_0) / W) ** 2))
+                * (-1 if n < 0.0 else 1)
+            )
         else:
             gamma += (
                 (R / (2 * pi))