1. Finite State Machines introduction to hunter-prey 10/8/10
PROJECT
introduction to hunter-prey
DATE
10/8/10
PRESENTERS
JOSEPH LEE, ALEX ZIRBEL

2. So I hear you like Graph Theory.

3. Introduction to Finite State Machines
Overview
Implementation in C
Hunter-Prey
An Example
Questions?

4. Introduction to Finite State Machines
Overview
Implementation in C
Hunter-Prey
An Example
Questions?

5. Overview Sometimes it is best to draw a diagram. Initial State State 1
Carnegie Mellon
Overview
Initial State
State 1
State 2
State 3
Sometimes it is best to draw a diagram.

6. Overview When in doubt, do this: 1. Draw Diagram (Design)
Carnegie Mellon
Overview
When in doubt, do this:
1. Draw Diagram (Design)
2. Then Code (Implement)
int state = 1
while(1) {
switch(state) {
case 1:
printf(“hello!\n”);
state++;
break;
case 2:
printf(“good-bye.\n”);
state--;
default:
printf(“AHH! You shouldn’t be here!\n”); }

7. Introduction to Finite State Machines
Overview
Implementation in C
Hunter-Prey
An Example
Questions?

8. Implementation in C while(1){ switch(state){ #define HUNTER 1
Carnegie Mellon
Implementation in C
A FSM in C consists of two parts:
A While Loop
while(1){
A Switch Statement
switch(state){
You should define your states
#define HUNTER 1

9. Implementation in C Code Example: #define PREY 0 #define HUNTER 1
Carnegie Mellon
Implementation in C
Code Example:
#define PREY 0
#define HUNTER 1
#define WAIT -1
...
int state = PREY;
while(1){
switch(state){
case PREY:
/* prey code */
break;
case WAIT:
/* waiting code */
case HUNTER:
/* hunter code */
default: break; }

10. Implementation in C Code Example: Define the states #define PREY 0
Carnegie Mellon
Implementation in C
Code Example:
#define PREY 0
#define HUNTER 1
#define WAIT -1
...
int state = PREY;
while(1){
switch(state){
case PREY:
/* prey code */
break;
case WAIT:
/* waiting code */
case HUNTER:
/* hunter code */
default: break; }
Define the states

11. Implementation in C Code Example: Make the while loop #define PREY 0
Carnegie Mellon
Implementation in C
Code Example:
#define PREY 0
#define HUNTER 1
#define WAIT -1
...
int state = PREY;
while(1){
switch(state){
case PREY:
/* prey code */
break;
case WAIT:
/* waiting code */
case HUNTER:
/* hunter code */
default: break; }
Make the while loop

12. Implementation in C Code Example: Add the switch statement
Carnegie Mellon
Implementation in C
Code Example:
#define PREY 0
#define HUNTER 1
#define WAIT -1
...
int state = PREY;
while(1){
switch(state){
case PREY:
/* prey code */
break;
case WAIT:
/* waiting code */
case HUNTER:
/* hunter code */
default: break; }
Add the switch statement

13. Implementation in C Code Example: You should have break statements
Carnegie Mellon
Implementation in C
Code Example:
#define PREY 0
#define HUNTER 1
#define WAIT -1
...
int state = PREY;
while(1){
switch(state){
case PREY:
/* prey code */
break;
case WAIT:
/* waiting code */
case HUNTER:
/* hunter code */
default: break; }
You should have
break statements

14. Implementation in C Things to look out for
Carnegie Mellon
Implementation in C
Things to look out for
Do not have states that go nowhere
Bad State
Conversely, do not have unreachable states
Bad State

15. Introduction to Finite State Machines
Overview
Implementation in C
Hunter-Prey
An Example
Questions?

16. Hunter-Prey The Prey has simple requirements
Carnegie Mellon
Hunter-Prey
The Prey has simple requirements
Design a prey that will run from the hunters
If the prey is tagged, it will first acknowledge the tag
After the prey acknowledges, it will change state to Waiting
After waiting, the bot will move to the Hunter state

17. Hunter-Prey The Hunter is just as simple
Carnegie Mellon
Hunter-Prey
The Hunter is just as simple
Design a hunter that will catch the prey
When the hunter is close enough to the prey, it will tag the prey
If the prey acknowledges the tag, then the hunter becomes the Prey
If another hunter becomes the prey, your hunter changes state to Waiting

18. Introduction to Finite State Machines
Overview
Implementation in C
Hunter-Prey
An Example
Questions?

19. An Example: Zombie Design
Carnegie Mellon
An Example: Zombie Design
hunting for
food
hiding in corners
blinded by light
Zombie becomes hungry
human shines
flashlight
Zombie
recovers
Zombie decides
hunting is not worth it

20. An Example: Zombie Implementation
Carnegie Mellon
An Example: Zombie Implementation
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
hunting for
food
case HUNTING:
//locate flesh
//go towards flesh
//grab blindly
break;
human shines
flashlight
case HUNTING:
//same as above
if(light_shine)
state=BLINDED;
break;

21. An Example: Zombie Implementation
Carnegie Mellon
An Example: Zombie Implementation
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else

22. An Example: Zombie Implementation
Carnegie Mellon
An Example: Zombie Implementation
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else

23. An Example: Zombie Implementation
Carnegie Mellon
An Example: Zombie Implementation
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else

24. An Example: Zombie Implementation
Carnegie Mellon
An Example: Zombie Implementation
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else

25. An Example: Tracing Zombie
Carnegie Mellon
An Example: Tracing Zombie
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else
state = HIDING
motivated = 0

26. An Example: Tracing Zombie
Carnegie Mellon
An Example: Tracing Zombie
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else
Before
state = HIDING
motivated = 0
After
state = HIDING
motivated = 1

27. An Example: Tracing Zombie
Carnegie Mellon
An Example: Tracing Zombie
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else
Before
state = HIDING
motivated = 1
After
state = HUNTING
motivated = 2

28. An Example: Tracing Zombie
Carnegie Mellon
An Example: Tracing Zombie
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else
Before
state = HUNTING
motivated = 2
After
state = BLINDED
motivated = 1

29. An Example: Tracing Zombie
Carnegie Mellon
An Example: Tracing Zombie
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else
Before
state = BLINDED
motivated = 1
After
state = HUNTING
motivated = 1

30. An Example: Tracing Zombie
Carnegie Mellon
An Example: Tracing Zombie
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else
Before
state = HUNTING
motivated = 1
After
state = BLINDED
motivated = 0

31. An Example: Tracing Zombie
Carnegie Mellon
An Example: Tracing Zombie
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else
Before
state = BLINDED
motivated = 0
After
state = HIDING
motivated = 0

32. An Example: Tracing Zombie
Carnegie Mellon
An Example: Tracing Zombie
#define HIDING 0
#define HUNTING 1
#define BLINDED 2
int main(){
int state = HIDING;
int motivated = 0;
while(1){
switch(state){
case HIDING:
motivated++;
if(motivated >= 2)
state = HUNTING;
break;
case HUNTING:
if(light_shine){
motivated--;
state = BLINDED; }
case BLINDED:
if(!motivated)
state = HIDING;
else
Before
state = HIDING
motivated = 0
After
state = HIDING
motivated = 1
Back to Square 1

33. Introduction to Finite State Machines
Overview
Implementation in C
Hunter-Prey
Going Further
Questions?