Count valid instead of invalid Rossby values

Simpler, no subtraction.

cost_function.py

@@ -38,7 +38,7 @@ def calculate_radii_rossby(list_eddies, e_overestim, handlers, array_d_init):
 
     radii = 0 # in m
     rossby = 0
-    days_modifier = 0
+    n_valid_Rossby = 0
     Omega = 2 * math.pi / 86164.
     n_eddies = len(list_eddies)
 
@@ -61,17 +61,15 @@ def calculate_radii_rossby(list_eddies, e_overestim, handlers, array_d_init):
             .record(location)['r_eq_area'] * 1000 # in m
 
         if (V_max < 100):
-            # calculate Ro and Delta_Ro
             rossby += V_max / (f * R_Vmax)
-        else:
-            days_modifier += 1
+            n_valid_Rossby += 1
 
         radii += R_Vmax # in m
 
     radii /= n_eddies
-
-    if n_eddies > days_modifier:
-        rossby /= n_eddies - days_modifier
+    
+    if n_valid_Rossby != 0:
+        rossby /= n_valid_Rossby
     else:
         rossby = None