Percolator Problem: Monte Carlo simulation

Quick-implementation

from pprint import pprint
import random
import time

NUM_ELEM = 600
NUM_SD = NUM_ELEM*NUM_ELEM 	#single dim
dyns = None
matrix = None
experiment_attempts = 2

class Cell:
	def __init__(self, i):
		self.parent = i
		self.index = i
		self.weight = 1
	def connect(self, node):
		self.parent = node.index
		self.weight += node.weight
		
def main():
	global dyns, matrix
	
	ratio_sum = 0
	start_time = time.time()
	for k in range(0, experiment_attempts):
		num_times = 0
		
		# 2-d actual matrix
		matrix = [[0 for i in range(NUM_ELEM)] for i in range(NUM_ELEM)]
	
		# structure 1-d
		dyns = [Cell(i) for i in range(NUM_SD)]
	
		for j in range(1, NUM_ELEM):
			connect(j, 0)
			connect(NUM_SD-j-1, NUM_SD-1)
		
		while(not is_percolated()):
			randint1 = random.randint(0, NUM_ELEM - 1)
			randint2 = random.randint(0, NUM_ELEM - 1)

			if site_open(randint1,randint2):
				num_times += 1
			
		ratio = float(num_times)/NUM_SD
		print(ratio)

		ratio_sum += ratio
	print "Final: ", ratio_sum/experiment_attempts
	print time.time() - start_time, "seconds"
	
def site_open(i, j):
	if matrix[i][j] == 1:
		return False
	else:
		matrix[i][j] = 1
		if i > 0 and matrix[i - 1][j] == 1:
			connect(compute_offset(i, j), compute_offset(i - 1, j))
		
		if j > 0 and matrix[i][j - 1] == 1:
			connect(compute_offset(i, j), compute_offset(i, j - 1))
			
		if i < (NUM_ELEM - 1) and matrix[i+1][j] == 1:
			connect(compute_offset(i, j), compute_offset(i + 1, j))
			
		if j < (NUM_ELEM - 1) and matrix[i][j + 1] == 1:
			connect(compute_offset(i, j), compute_offset(i, j + 1))
			
		return True

def compute_offset(i, j):
	return (i*NUM_ELEM + j)
	
	
def connect(i, j):
	var1 = root(i)
	var2 = root(j)
	
	if(var1 == var2):
		return False

	if(var1.weight <= var2.weight):
		var1.connect(var2)
	else:
		var2.connect(var1)
	
def root(i):
	node = dyns[i]
	while(node.parent!=node.index):
		node = dyns[node.parent]
	return node
	
def is_connected(i, j):
	return root(i) == root(j)
	
def get_dyns():
	ret = {}
	i = 0
	for dyn in dyns:
		ret[i] = dyn.parent.index
		i += 1
	return ret
		
def is_percolated():
	return is_connected(0, NUM_SD - 1)
		
if __name__ == '__main__':
	main()