Create function `date_eddy_to_node`

Convert_Matlab/convert_id.py

@@ -18,3 +18,10 @@ def node_to_date_eddy(node_index, e_overestim, d_init):
     return {"eddy_index": node_index - k * e_overestim, "date_index": k,
             "days_1950": d,
             "date": datetime.date(1950, 1, 1) + datetime.timedelta(d)}
+
+def date_eddy_to_node(d, eddy_index, e_overestim, d_init):
+    """Convert from eddy identification in shapefiles to node
+    identification in graph.
+
+    """
+    return (d- d_init) * e_overestim + eddy_index