test and fix vanGenuchten implementation

LDDsimulation/functions.py

@@ -131,13 +131,12 @@ def vanGenuchten_S_sym(pc, n_index, alpha):
 
 # derivative of S-pc relationship with respect to pc. This is needed for the
 # construction of a analytic solution.
-def vanGenuchten_S_prime(pc, n_index, alpha):
+def vanGenuchten_S_prime_sym(pc, n_index, alpha):
     # inverse capillary pressure-saturation-relationship
     enumerator = -1.0*(alpha*(n_index - 1)*(alpha*pc)**(n_index - 1))
     denominator = ((1 + (alpha*pc)**n_index)**((2*n_index - 1)/n_index))
     return enumerator/denominator
 
-
 def generate_Spc_dicts(
         Spc_on_subdomains: tp.Dict[int, tp.Dict[str, tp.Dict[str, float]]]
         )-> tp.Dict[str, tp.Dict[int, tp.Callable]]: