A Simplified Schelling Model
December 2, 2013I coded up a simplified version of the Schelling segregation model today. I thought I'd share the code below.
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| import random | |
| neighborhood = 2 # cells on both sides | |
| happy = 2 # at least this many cells are same | |
| empty = .1 | |
| red = .45 | |
| blue = .45 | |
| numcells = 80 | |
| trials = 1000 | |
| def create_city(n): | |
| city = [] | |
| for i in range(n): | |
| x = random.random() | |
| if x < empty: | |
| cell = ' ' | |
| elif x < empty+red: | |
| cell = '+' | |
| else: | |
| cell = '.' | |
| city.append(cell) | |
| return city | |
| def print_city(city): | |
| print ''.join(city) | |
| def iterate(city): | |
| # choose random cell | |
| cell = random.randint(0, len(city)-1) | |
| # determine if happy | |
| # if so, do nothing | |
| if not cell_is_happy(cell, city): | |
| # else, move to random empty cell | |
| empties = [x for x in range(len(city)) if city[x] == ' '] | |
| destination = empties[random.randint(0, len(empties)-1)] | |
| city[destination] = city[cell] | |
| city[cell] = ' ' | |
| def cell_is_happy(cell, city): | |
| # cell is an index into city | |
| type = city[cell] | |
| count = 0 | |
| for i in range(1, neighborhood+1): | |
| if city[cell-i] == type: count += 1 | |
| if cell+i >= len(city): | |
| if city[len(city)-cell+i] == type: count += 1 | |
| else: | |
| if city[cell+i] == type: count += 1 | |
| return count >= happy | |
| def main(): | |
| city = create_city(numcells) | |
| print_city(city) | |
| for i in range(trials): | |
| iterate(city) | |
| print_city(city) | |
| print 'Done' | |
| if __name__=='__main__': | |
| main() |
Here's some output (with numcells above changed to 40):
+.++++++ .+.+.....++.++....++...++....+..+.. ++.++ +.++++++ .+.+.....++.++....++...++....+..+.. ++.++ +.++++++ .+.+.....++.++....++...++....+..+.. ++.++ +.+++++++.+.+.....++.+ ....++...++....+..+.. ++.++ +.+++++++.+.+.....++.+ ....++...++....+..+.. ++.++ +.+++++++.+.+.....++.+ ....++...++....+..+.. ++.++ +.+++++++.+.+.....++.+ ....++...++....+..+.. ++.++ +.+++++++.+.+.....++.+ ....++...++....+..+.. ++.++ +.+++++++.+.+.....++.+ ....++...++....+..+. .++.++ +.+++++++.+.+.....++.+ ....++...++....+..+. .++.++ <...snip...> +++++++++++++......++++....+ ... +............++++ +++++++++++++......++++....+ ... +............++++ +++++++++++++......++++....+ ... +............++++ +++++++++++++......++++....+ ... +............++++ Done
Pretty neat -- it works! I love complexity.