Transition. Erf fitting. first/last datetime now optional

cfatools/tsanalyser/transition.py

@@ -221,14 +221,18 @@ def get_transition_duration_gauss_sigma(df: pd.DataFrame,
 
 
 def get_transition_duration_erf(df: pd.DataFrame,
-                                first_datetime: datetime.datetime,
-                                last_datetime: datetime.datetime,
+                                first_datetime: datetime.datetime = None,
+                                last_datetime: datetime.datetime = None,
                                 col_value_name: str = "value",
                                 debug_plot: bool = False) -> float:
-    # Restrict the data to the transition area
-    df = df[(df.index >= first_datetime) & (df.index <= last_datetime)]
     df = df.copy()
 
+    # Restrict the data to the transition area
+    if first_datetime is not None:
+        df = df[df.index >= first_datetime]
+    if last_datetime is not None:
+        df = df[df.index <= last_datetime]
+
     def erfunc(x, C1, C2, z0, sigma):
         return (C1/2) * (1 + erf((x - z0) / (sigma * np.sqrt(2)))) + C2