Bug fix: interpret Matlab serial date number

[Matlab serial date
number](https://fr.mathworks.com/help/matlab/ref/datenum.html) is the
number of days from Jan 1st, year 0, in a proleptic gregorian
calendar.

Analysis/make_graph_from_Matlab.py

@@ -4,6 +4,7 @@
     and all the anticyclones are processed before all the cyclones."""
 
 import scipy.io as sio
+import datetime
 
 def convert_id(orientation, eddy_index_Matlab):
     """Convert from Matlab eddy identification to eddy
@@ -17,7 +18,10 @@ def convert_id(orientation, eddy_index_Matlab):
     """
 
     k = (eddy_index_Matlab - 1) // n_max
-    date = Assoc_eddies_Anti_max["date_num"][k]
+    date = datetime.date.fromordinal(Assoc_eddies_Anti_max["date_num"][k]
+                                     - 366) - datetime.date(1950,1,1)
+    date = date.days
+    
     if orientation == "anticyclone":
         eddy_index_F = eddy_index_Matlab - k * n_max
     else: