Remove intermediary variables

Remove intermediary variables `first_term`, `second_term`, `third_term`.

Trajectories/cost_function.py

@@ -196,7 +196,6 @@ for edge in g.edges():
     Delta_Cent = math.sqrt((lon_diff * 111.32 * math.cos(lat_for_conv))**2
                            + ((g.vp.pos_last[source_node][1]
                                - g.vp.pos_first[target_node][1]) * 110.574)**2)
-    first_term = ((Delta_Cent - delta_cent_mean)/delta_cent_std)**2
 
     # Rossbies:
     if (g.vp.first_av_ros[target_node] and g.vp.last_av_ros[source_node]):
@@ -206,16 +205,15 @@ for edge in g.edges():
         # At least one of the rossbies is invalid.
         Delta_Ro = 0
 
-    second_term = ((Delta_Ro - delta_ro_mean)/delta_ro_std)**2
-
     # R_Vmax 1 and 2 already exist, just get the delta
     Delta_R_Vmax = g.vp.last_av_rad[source_node] \
         - g.vp.first_av_rad[target_node]
 
-    third_term = ((Delta_R_Vmax - delta_r_mean)/delta_r_std)**2
-
     # Calculate the cost function and assign as weight to the edge:
-    g.ep.cost_function[edge] = math.sqrt(first_term + second_term + third_term)
+    g.ep.cost_function[edge] \
+        = math.sqrt(((Delta_Cent - delta_cent_mean) / delta_cent_std)**2
+                    + ((Delta_Ro - delta_ro_mean) / delta_ro_std)**2
+                    + ((Delta_R_Vmax - delta_r_mean) / delta_r_std)**2)
 
 t1 = time.perf_counter()
 timings.write(f"iterating on edges: {t1 - t0:.0f} s\n")