Programming for Social Scientists Lecture 5 UCLA Political Science 209-1: Programming for Social...

Programming for Social Scientists

Lecture 5UCLA Political Science 209-1: Programming for Social

Scientists

Winter 1999

Lars-Erik Cederman & Benedikt Stefansson

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

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

Arrays and Linked Lists

3 18 2 5 7 4 9 27

Array: fast access

3 8 2 5

Linked list: flexibility


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

SimpleList

• Create 10 elements in a linked list

• Print them

• Repeat 10 times:– Scramble the order– Print the elements again


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

SimpleList: File Structure

main.mModel-

Swarm.m Element.m

Element.hModel-Swarm.h


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

SimpleList: Element.h/m

// Element.h

#import <objectbase.h>

#import <objectbase/SwarmObject.h>

@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

SimpleList: ModelSwarm.h#import "Element.h"


#import <objectbase/Swarm.h>

#import <random.h>

@interface ModelSwarm: Swarm {

id objList;

}

+createBegin: (id) aZone;

-createEnd;

-buildObjects: (int) n;

-printObjects: list;

-shuffle: list;

-run;

@end


12

SimpleList: ModelSwarm.m (1)


@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


-printObjects: list {

id index, anElement;

index = [list begin: self];

while ((anElement=[index next]))

printf("%d ", [anElement getID]);

[index drop];

printf("\n");

return self;

}


14


-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


-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

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

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

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

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

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...)

MT19937Generator

UniformInteger

UniformUnsigned

Integer

UniformDouble


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

Looking up documentationMain 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...

MethodsPhase: Creating

Phase: Using

-(BOOL)getCount

-(BOOL)contains: aMember


23

Evol IPD

• To manage more than two players we add a playerList

• Tournament is a nested swarm letting two agents play IPD

main

ModelSwarmpopList

Tournament

newListwinner


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

Evol IPD: File Structure

main.mModel-

Swarm.mTourna-ment.m

Tourna-ment.h

Model-Swarm.h

Player.m

Player.h


26

Evol IPD: main.m#import <simtools.h>


int main(int argc, const char ** argv) {

id modelSwarm;

initSwarm(argc, argv);

modelSwarm = [ModelSwarm create: globalZone];

[modelSwarm buildObjects];

[modelSwarm run];

return 0;

}


27

Evol IPD: ModelSwarm.h#import "Player.h"

#import "Tournament.h"


#import <objectbase/SwarmObject.h>

#import <space.h>

#import <activity.h>

#import <random.h>

@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

Evol IPD: ModelSwarm.m (1)#import "ModelSwarm.h"

#import <simtools.h>

@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

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

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

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

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

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

Evol IPD: Tournament.h

#import "Player.h"#import <objectbase.h>#import <objectbase/Swarm.h>#import <space.h>#import <activity.h>

@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

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

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

• The model.setup file:@beginrandomSeed 8251777selectionPressure 0.75numGen 15n0 64n1 64n2 64n3 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"];

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