1. Programming for Social Scientists Lecture 5 UCLA Political Science 209-1: Programming for Social Scientists Winter 1999 Lars-Erik Cederman & Benedikt Stefansson

2. POL SCI 209-1 Cederman / Stenfansson 2 Today's topics lists of agents random number generators loading parameters from file nested Swarms Example 1: SimpleList Example 2: Evol IPD (evolutionary version of SimpleIPD)

3. POL SCI 209-1 Cederman / Stenfansson 3 Managing many agents Swarm offers the class Collection Collections can be of type: –List (today's focus!) –Array (different from arrays in C!) –Keyed Collection (maps and sets) Note: Collections are dynamic data structures that can change during run-time (cf. pointers in C)

4. POL SCI 209-1 Cederman / Stenfansson 4 Arrays and Linked Lists 3182574927 Array: fast access 3 8 2 5 Linked list: flexibility

5. POL SCI 209-1 Cederman / Stenfansson 5 Lists in Swarm obj1 obj2 obj3 obj4 list = [List create: self] [list atOffset: 3] index = [list begin: self] obj=[index next] [list addLast: obj4]

6. POL SCI 209-1 Cederman / Stenfansson 6 SimpleList Create 10 elements in a linked list Print them Repeat 10 times: –Scramble the order –Print the elements again

7. POL SCI 209-1 Cederman / Stenfansson 7 SimpleList: Sample Output Count: 10 List: 0 1 2 3 4 5 6 7 8 9 Repl 1: 8 2 0 1 4 7 9 3 5 6 Repl 2: 9 0 3 6 5 1 8 2 4 7... Repl 10:...

8. POL SCI 209-1 Cederman / Stenfansson 8 SimpleList: File Structure main.m Model- Swarm.m Element.m Element.h Model- Swarm.h

9. POL SCI 209-1 Cederman / Stenfansson 9 SimpleList: main.m #import "ModelSwarm.h" int main(int argc, const char ** argv) { id modelSwarm; initSwarm(argc, argv); modelSwarm = [ModelSwarm create: globalZone]; [modelSwarm buildObjects: 10]; [modelSwarm run]; return 0; }

10. POL SCI 209-1 Cederman / Stenfansson 10 SimpleList: Element.h/m // Element.h #import @interface Element: SwarmObject { int name; } -init: (int) n; -(int) getID; @end // Element.m #import "Element.h" @implementation Element -init: (int) n { name = n; return self; } -(int) getID { return name; } @end

11. POL SCI 209-1 Cederman / Stenfansson 11 SimpleList: ModelSwarm.h #import "Element.h" #import @interface ModelSwarm: Swarm { id objList; } +createBegin: (id) aZone; -createEnd; -buildObjects: (int) n; -printObjects: list; -shuffle: list; -run; @end

12. POL SCI 209-1 Cederman / Stenfansson 12 SimpleList: ModelSwarm.m (1) #import "ModelSwarm.h" @implementation ModelSwarm +createBegin: (id) aZone { ModelSwarm * obj; obj = [super createBegin: aZone]; return obj; } -createEnd { return [super createEnd]; } -buildObjects: (int) n { int i; id anElement; objList = [List create:self]; for (i=0; i<n; i++) { anElement = [Element create: self]; [anElement init: i]; [objList addLast: anElement]; } return self; }

13. POL SCI 209-1 Cederman / Stenfansson 13 SimpleList: ModelSwarm.m (2) -printObjects: list { id index, anElement; index = [list begin: self]; while ((anElement=[index next])) printf("%d ", [anElement getID]); [index drop]; printf("\n"); return self; }

14. POL SCI 209-1 Cederman / Stenfansson 14 SimpleList: ModelSwarm.m (3) -shuffle: list { int j, k; id temp; j = [list getCount]; while (j>1) { k = [uniformIntRand getIntegerWithMin: 0 withMax: j-1]; j--; temp = [list atOffset: k]; [list atOffset: k put: [list atOffset: j]]; [list atOffset: j put: temp]; } return self; }

15. POL SCI 209-1 Cederman / Stenfansson 15 SimpleList: ModelSwarm.m (4) -run { int randomSeed; printf("Count: %d\n", [objList getCount]); printf("List: "); [self printObjects: objList]; for (randomSeed=1; randomSeed<=10; randomSeed++) { [randomGenerator setStateFromSeed: randomSeed]; [self shuffle: objList]; printf("Repl %2d: ", randomSeed); [self printObjects: objList]; } return self; } @end

16. POL SCI 209-1 Cederman / Stenfansson 16 Some Collection syntax getCount –Gives number of members atOffset: i –Retrieves member at location i atOffset:i put: obj –Inserts obj at location i addFirst: o addLast: o –Adds o at start/end of list getFirst,getLast –Returns first/last member contains: o –Returns 1 if o is member remove: o –Removes object o removeAll –Removes all forEach:M(message) –Sends message to all members removeFirst/Last –removes and returns first/last member

17. POL SCI 209-1 Cederman / Stenfansson 17 Accessing Collections with Index Any collection can generate an index of itself The index behaves as an object, and understands messages such as: –prev,next –findNext: o,findPrev: o Using index to loop over all members: index=[list begin: zone]; while(o=[index next]) value=[o getValue]; [index drop];

18. POL SCI 209-1 Cederman / Stenfansson 18 Typical use of List Typical use of a List instance is to keep track of agent population At create time Model initializes each agent and puts him on agentList The agentList is then accessed by Schedule, GUI objects and so on... Example for(i=0;i<numAgents;i++) { a=[Agent create: zone]; [a setVar1: var1]; [a setVar2: var2];... [a setVarN: varN]; [agentList addLast: a]; }

19. POL SCI 209-1 Cederman / Stenfansson 19 Generating Random Numbers To draw random numbers from a distribution you’ll need –a generator random seed - an integer number which primes the generator –a distribution Generator Distribution a seed random sequence of numbers

20. POL SCI 209-1 Cederman / Stenfansson 20 Default distributions When calling initSwarm in main, three default distributions are generated, fed by a default generator It is also possible to choose other generators and distributions by using the Random library (more about that later...) MT19937 Generator Uniform Integer Uniform Unsigned Integer Uniform Double

21. POL SCI 209-1 Cederman / Stenfansson 21 Using the default distributions Default distributions are global Can call any distribution from any agent For a double in interval [minVal, maxVal]: [uniformDblRand getDoubleWithMin: minVal withMax: maxVal]; For an integer in interval [minVal, maxVal]: [uniformIntegerRand getDoubleWithMin: minVal withMax:maxVal]; To set the seed to Val: [randomGenerator setStateFromSeed: Val];

22. POL SCI 209-1 Cederman / Stenfansson 22 Looking up documentation Main resource: http://www.santafe.edu/projects/swarm/ Reference manual: e.g. Collections, Random libraries; see also index See e.g. Collection [p. 94]: Name Collection Description... Protocols adopted by Collection: Create,... Copy, Drop... Methods Phase: Creating Phase: Using -(BOOL)getCount -(BOOL)contains: aMember

23. POL SCI 209-1 Cederman / Stenfansson 23 Evol IPD To manage more than two players we add a playerList Tournament is a nested swarm letting two agents play IPD main ModelSwarm popList Tournament newList winner

24. POL SCI 209-1 Cederman / Stenfansson 24 Riolo's GA algorithm in pseudo- code (see Sci. Am.) while (NewPopNotFull) { i=random()/PopSize; j=random()/PopSize; if (URand01() < 0.75) Copy most fit of Pop[i],Pop[j] to NewPop else Copy least fit of Pop[i],Pop[j] to NewPop; } Pop = NewPop;

25. POL SCI 209-1 Cederman / Stenfansson 25 Evol IPD: File Structure main.m Model- Swarm.m Tourna- ment.m Tourna- ment.h Model- Swarm.h Player.m Player.h

26. POL SCI 209-1 Cederman / Stenfansson 26 Evol IPD: main.m #import #import "ModelSwarm.h" int main(int argc, const char ** argv) { id modelSwarm; initSwarm(argc, argv); modelSwarm = [ModelSwarm create: globalZone]; [modelSwarm buildObjects]; [modelSwarm run]; return 0; }

27. POL SCI 209-1 Cederman / Stenfansson 27 Evol IPD: ModelSwarm.h #import "Player.h" #import "Tournament.h" #import @interface ModelSwarm: Swarm { id popList,newList; int numGen, randomSeed; int numPlayers, num[4], n0, n1, n2, n3; double selectionPressure; } +createBegin: (id) aZone; -createEnd; -buildObjects; -runTournament; -reportResults: (int)gen; -run; @end

28. POL SCI 209-1 Cederman / Stenfansson 28 Evol IPD: ModelSwarm.m (1) #import "ModelSwarm.h" #import @implementation ModelSwarm +createBegin: (id) aZone { ModelSwarm * obj; obj = [super createBegin: aZone]; obj->numGen = 10; return obj; } -createEnd { [ObjectLoader load: self fromFileNamed: "model.setup"]; return [super createEnd]; }

29. POL SCI 209-1 Cederman / Stenfansson 29 Evol IPD: ModelSwarm (2) -buildObjects { id aPlayer; int pt,i; [randomGenerator setStateFromSeed: randomSeed]; time = 0; num[0] = n0; num[1] = n1; num[2] = n2; num[3] = n3; numPlayers = n0+n1+n2+n3; popList = [List create: self]; newList = [List create: self]; for (pt = 0; pt < 4; pt++) for (i = 0; i < num[pt]; i++) { aPlayer = [Player createBegin: self]; [aPlayer setPlayerType: pt]; aPlayer = [aPlayer createEnd]; [popList addLast: aPlayer]; } return self; }

30. POL SCI 209-1 Cederman / Stenfansson 30 Evol IPD: ModelSwarm.m (3) -runTournament { id tournament; id tempList; id player1, player2, survivor, newPlayer; int i, p1, p2; for (i=0; i<numPlayers; i++) { p1 = [uniformIntRand getIntegerWithMin: 0 withMax: numPlayers-1]; p2 = [uniformIntRand getIntegerWithMin: 0 withMax: numPlayers-1]; player1 = [popList atOffset: p1]; player2 = [popList atOffset: p2]; tournament = [Tournament createBegin: self]; [tournament setPlayer1: player1 Player2: player2]; [tournament createEnd]; [tournament run]; // for loop cont'd

31. POL SCI 209-1 Cederman / Stenfansson 31 Evol IPD: ModelSwarm.m (4) if ([uniformDblRand getDoubleWithMin: 0.0 withMax: 1.0] < selectionPressure) survivor=[tournament getWinner]; else survivor=[tournament getLoser]; newPlayer=[Player create: self]; [newPlayer initPlayerType: [survivor getPlayerType]]; [newList addLast: newPlayer]; } [tournament drop]; [popList deleteAll]; // Swapping lists tempList = popList; popList = newList; newList = tempList; return self; }

32. POL SCI 209-1 Cederman / Stenfansson 32 Evol IPD: ModelSwarm.m (5) -reportResults: (int) gen { id index; id aPlayer; int pt; for (pt=0; pt<4; pt++) num[pt] = 0; index = [popList begin: self]; while((aPlayer=[index next])) num[[aPlayer getPlayerType]]++; [index drop]; printf("Time: %4d Num: %6d %6d %6d %6d\n", gen, num[0], num[1], num[2], num[3]); return self; }

33. POL SCI 209-1 Cederman / Stenfansson 33 Evol IPD: ModelSwarm.m (6) -run { int gen; [self reportResults: 0]; for (gen = 1; gen <= numGen; gen++) { [self runTournament]; [self reportResults: gen]; } return self; } @end

34. POL SCI 209-1 Cederman / Stenfansson 34 Evol IPD: Tournament.h #import "Player.h" #import @interface Tournament: Swarm { id player1, player2; int numIter; } +createBegin: (id) aZone; -createEnd; -setPlayer1: p1 Player2: p2; -updateMemories; -distrPayoffs; -(id)getWinner; -(id)getLoser; -run; @end

35. POL SCI 209-1 Cederman / Stenfansson 35 Evol IPD: Tournament.m... @implementation Tournament... -setPlayer1: p1 Player2: p2... -updateMemories... -distrPayoffs... -(id)getWinner { int winner; if ([player1 getPayoff] > [player2 getPayoff]) winner = player1; else winner = player2; return winner; } -(id)getLoser... -run { int time; numIter = 4; [player1 setPayoff: 0]; [player2 setPayoff: 0]; for (time=0; time<numIter; time++) { [self updateMemories]; [player1 step: time]; [player2 step: time]; [self distrPayoffs]; } return self; }

36. POL SCI 209-1 Cederman / Stenfansson 36 Evol IPD: Player.m... int iParam[4] = {1, 1, 0, 0}; int pParam[4] = {1, 1, 0, 0}; int qParam[4] = {1, 0, 1, 0}; @implementation Player -setPlayerType: (int) pt { type = pt; return self; } -(int) getPlayerType { return type; }... -step: (int) time { if (time==0) newAction = iParam[type]; else { if (memory==1) newAction = pParam[type]; else newAction = qParam[type]; }; return self; } @end

37. POL SCI 209-1 Cederman / Stenfansson 37 The model.setup file: @begin randomSeed 8251777 selectionPressure 0.75 numGen 15 n0 64 n1 64 n2 64 n3 64 @end ObjectLoader needs –target object –name of file Loading/Saving state ObjectLoader –Reads values of ivars from file ObjectSaver –Writes values of ivars to file Any instance vars not mentioned in infile unchanged [ObjectLoader load: self fromFileNamed:"model.setup"];