def flip(x, p = p, q = q, m = m):
if rng.flip(p, q):
y = m[rng.random() % len(m)]
if rng.flip(1, 2):
return x + y
return x - y
return x
def cross(l1, l2, p):
"""cross(list, list, probability) -> list
Take elements from one list until a crossover is made, then take
elements from the other list, and so on, with the given probability
of a crossover at each position. The initial list is chosen at
random from one of the two lists with equal probability. The lists
must be the same length."""
l = [0] * len(l1)
x = map(None, l1, l2)
j = rng.random() % 2
(p, q) = torat(p)
for i in xrange(len(l1)):
if rng.flip(p, q):
j = 1 - j
l[i] = x[i][j]
return l
