add HN model with independent slopes

src/nmreval/models/bds.py

@@ -54,10 +54,31 @@ class HavriliakNegamiBDS(_AbstractBDS):
     name = 'Havriliak-Negami'
     equation = r'\Delta\epsilon / [1-(i\omega\tau)^{\gamma}]^{\alpha}'
     params = _AbstractBDS.params + [r'\alpha', r'\gamma']
-    bounds = _AbstractBDS.bounds + [(0, 1), (0, 1)]
+    bounds = _AbstractBDS.bounds + [(0, 1), (0, None)]
     susceptibility = HavriliakNegami.susceptibility
 
 
+class HavriliakNegamiAlphaGammaBDS:
+    type = 'Dielectric Spectroscopy'
+    name = 'Havriliak-Negami (ind. slopes)'
+    equation = r'\Delta\epsilon / [1-(i\omega\tau)^{\gamma}]^{\alpha}'
+    params = [r'\Delta\epsilon', r'\tau_{0}', r'\alpha', r'\alpha\gamma']
+    bounds = [(0, None), (0, None), (0, 1), (0, 1)]
+    iscomplex = True
+
+    @staticmethod
+    def func(x, deps, tau, alpha, alphagamma, complex_mode: int = 0, **kwargs):
+        chi = deps * HavriliakNegami.susceptibility(2*np.pi*x, tau, alpha, alphagamma/alpha, **kwargs)
+        if complex_mode == 0:
+            return chi
+        elif complex_mode == 1:
+            return chi.real
+        elif complex_mode == 2:
+            return chi.imag
+        else:
+            raise ValueError(f'{complex_mode!r} is not 0, 1, 2')
+
+
 class KWWBDS(_AbstractBDS):
     name = 'KWW'
     params = _AbstractBDS.params + [r'\beta']