diff --git a/week09/improvement/boids.py b/week09/improvement/boids.py
index e1cba89..f329db7 100644
--- a/week09/improvement/boids.py
+++ b/week09/improvement/boids.py
@@ -1,44 +1,71 @@
 """
-A deliberately bad implementation of 
+An improved implementation of 
 [Boids](http://dl.acm.org/citation.cfm?doid=37401.37406)
 for use as an exercise on refactoring.
 
 This code simulates the swarming behaviour of bird-like objects ("boids").
-"""
 
-from matplotlib import pyplot as plt
-from matplotlib import animation
+Aspects of boid motion simulated:
+1. Boids want to fly towards centre of flock
+2. Boids want to fly away from nearby boids
+3. Boids want to have similar velocity to nearby boids
+"""
 
+# import random for definining boids' initial states
 import random
 
-boids_x=[random.uniform(-450,50.0) for x in range(50)]
-boids_y=[random.uniform(300.0,600.0) for x in range(50)]
-boid_x_velocities=[random.uniform(0,10.0) for x in range(50)]
-boid_y_velocities=[random.uniform(-20.0,20.0) for x in range(50)]
-boids=(boids_x,boids_y,boid_x_velocities,boid_y_velocities)
+# set number of boids
+num_boids = 50
+xmin = -450
+xmax = 50
+ymin = 60
+ymax = 300
+xvmin = 0
+xvmax = 10
+yvmin = -20
+yvmax = 20
+
+# create boids within function using user-defined values
+def create_boids(num_boids,xmin,xmax,ymin,ymax,xvmin,xvmax,yvmin,yvmax):
+    # produce list of each variable
+    boids_x=[random.uniform(xmin,xmax) for x in range(num_boids)]
+    boids_y=[random.uniform(ymin,ymax) for x in range(num_boids)]
+    boid_x_velocities=[random.uniform(xvmin,xvmax) for x in range(num_boids)]
+    boid_y_velocities=[random.uniform(yxmin,yvmax) for x in range(num_boids)]
+    # produce tuple of variable lists
+    boids=(boids_x,boids_y,boid_x_velocities,boid_y_velocities)
+    return boids
 
-def update_boids(boids):
+boids = create_boids(num_boids,xmin,xmax,ymin,ymax,xvmin,xvmax,yvmin,yvmax)
+
+# define variables for updating
+centre_scale = 0.01
+local_vel_scale = 0.125
+repel_thresh = 100
+local_vel_thresh = 10000
+
+def update_boids(boids, centre_scale, local_vel_scale, repel_thresh, local_vel_thresh):
+    # define positions and velocities of boids
+    # xs - list of boid x positions
+    # ys - list of boid y positions
+    # xvs - list of boid x velocities
+    # yvs - list of boid y velocities
     xs,ys,xvs,yvs=boids
-    # Fly towards the middle
-    for i in range(len(xs)):
-        for j in range(len(xs)):
-            xvs[i]=xvs[i]+(xs[j]-xs[i])*0.01/len(xs)
-    for i in range(len(xs)):
-        for j in range(len(xs)):
-            yvs[i]=yvs[i]+(ys[j]-ys[i])*0.01/len(xs)
-    # Fly away from nearby boids
+    # simulate different aspects of boid motion
     for i in range(len(xs)):
+        # iterate over all other boids to define interactions
         for j in range(len(xs)):
-            if (xs[j]-xs[i])**2 + (ys[j]-ys[i])**2 < 100:
+            # Fly towards the middle (1)
+            xvs[i]=xvs[i]+(xs[j]-xs[i])*centre_scale/len(xs)
+            yvs[i]=yvs[i]+(ys[j]-ys[i])*centre_scale/len(xs)
+            # Fly away from nearby boids (2)
+            if (xs[j]-xs[i])**2 + (ys[j]-ys[i])**2 < repel_thresh:
                 xvs[i]=xvs[i]+(xs[i]-xs[j])
                 yvs[i]=yvs[i]+(ys[i]-ys[j])
-    # Try to match speed with nearby boids
-    for i in range(len(xs)):
-        for j in range(len(xs)):
-            if (xs[j]-xs[i])**2 + (ys[j]-ys[i])**2 < 10000:
-                xvs[i]=xvs[i]+(xvs[j]-xvs[i])*0.125/len(xs)
-                yvs[i]=yvs[i]+(yvs[j]-yvs[i])*0.125/len(xs)
-    # Move according to velocities
-    for i in range(len(xs)):
+             # Try to match speed with nearby boids (3)
+            if (xs[j]-xs[i])**2 + (ys[j]-ys[i])**2 < local_vel_thresh:
+                xvs[i]=xvs[i]+(xvs[j]-xvs[i])*local_vel_scale/len(xs)
+                yvs[i]=yvs[i]+(yvs[j]-yvs[i])*local_vel_scale/len(xs)
+        # Move according to velocities
         xs[i]=xs[i]+xvs[i]
         ys[i]=ys[i]+yvs[i]
\ No newline at end of file
diff --git a/week09/refactoring/initial_global.py b/week09/refactoring/initial_global.py
index 21f1323..e3e223c 100644
--- a/week09/refactoring/initial_global.py
+++ b/week09/refactoring/initial_global.py
@@ -1,16 +1,16 @@
-def average_age():
+def average_age(group):
     """Compute the average age of the group's members."""
     all_ages = [person["age"] for person in group.values()]
     return sum(all_ages) / len(group)
 
 
-def forget(person1, person2):
+def forget(group, person1, person2):
     """Remove the connection between two people."""
     group[person1]["relations"].pop(person2, None)
     group[person2]["relations"].pop(person1, None)
 
 
-def add_person(name, age, job, relations):
+def add_person(group, name, age, job, relations):
     """Add a new person with the given characteristics to the group."""
     new_person = {
         "age": age,
@@ -19,8 +19,8 @@ def add_person(name, age, job, relations):
     }
     group[name] = new_person
 
-
-group = {
+if __name__ == "__main__":
+    group = {
     "Jill": {
         "age": 26,
         "job": "biologist",
@@ -43,19 +43,18 @@ def add_person(name, age, job, relations):
             "Jill": "partner"
         }
     }
-}
+    }   
 
-nash_relations = {
+    nash_relations = {
     "John": "cousin",
     "Zalika": "landlord"
-}
+    }
 
-add_person("Nash", 34, "chef", nash_relations)
+    add_person(group, "Nash", 34, "chef", nash_relations)
 
-forget("Nash", "John")
+    forget(group, "Nash", "John")
 
-if __name__ == "__main__":
     assert len(group) == 4, "Group should have 4 members"
-    assert average_age() == 28.75, "Average age of the group is incorrect!"
+    assert average_age(group) == 28.75, "Average age of the group is incorrect!"
     assert len(group["Nash"]["relations"]) == 1, "Nash should only have one relation"
     print("All assertions have passed!")