dummy polarization index function

rowers/metrics.py

@@ -359,6 +359,9 @@ This value should be fairly constant across all stroke rates.""",
     )
 
 
+def polarization_index(df,rower):
+    return 0
+
 def calc_trimp(df,sex,hrmax,hrmin,hrftp):
     if sex == 'male':
         f = 1.92