# Population simulation leads to Valentine’s Day a[R]t

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Working on a quick-and-dirty simulation of people wandering around until they find neighbors, then settling down. After playing with the coloring a bit I arrived at the above image, which I quite like. Code below:

# Code by Matt Asher for statisticsblog.com # Feel free to modify and redistribute, but please keep this notice maxSettlers = 150000 # Size of the area areaW = 300 areaH = 300 # How many small movements will they make to find a neighbor maxSteps = 200 # Homesteaders, they don't care about finding a neighbor numbHomesteaders = 10 areaMatrix = matrix(0, nrow=areaW, ncol=areaH) # For the walk part adjacents = array(c(1,0,1,1,0,1,-1,1,-1,0,-1,-1,0,-1,1,-1), dim=c(2,8)) # Is an adjacent cell occupied? hasNeighbor <- function(m,n,theMatrix) { toReturn = FALSE for(k in 1:8) { yCheck = m + adjacents[,k][1] xCheck = n + adjacents[,k][2] if( !((xCheck > areaW) | (xCheck < 1) | (yCheck > areaH) | (yCheck < 1)) ) { if(theMatrix[yCheck,xCheck]>0) { toReturn = TRUE } } } return(toReturn) } # Main loop for(i in 1:maxSettlers) { steps = 1 xPos = sample(1:areaW, 1) yPos = sample(1:areaH, 1) if(i <= numbHomesteaders) { # Seed it with homesteaders areaMatrix[xPos,yPos] = 1 } else { if(areaMatrix[xPos,yPos]==0 & hasNeighbor(xPos,yPos,areaMatrix)) { areaMatrix[xPos,yPos] = 1 } else { spotFound = FALSE outOfBounds = FALSE while(!spotFound & !outOfBounds & (steps<maxSteps)) { # Look for a new location in one of adjacent 9 cells, while still in area steps = steps + 1 movement = adjacents[,sample(1:8,1)] xPos = xPos + movement[1] yPos = yPos + movement[2] if( (xPos > areaW) | (xPos < 1) | (yPos > areaH) | (yPos < 1)) { outOfBounds = TRUE } else if(hasNeighbor(xPos,yPos,areaMatrix) ) { areaMatrix[xPos,yPos] = steps spotFound = TRUE } } } } } image(areaMatrix, col=rev(rgb(seq(0.01,1,0.01),seq(0.01,1,0.01),seq(0.01,1,0.01)))) # I think this version looks nicer! # areaMatrix[areaMatrix !=0] = 1 # image(areaMatrix, col=rev(rgb(.5,0,seq(0.2,1,0.2))))

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