def sjt_local(pi, inv, x):
# The goal of local(pi, inv, i) is to move i permutation pi with inverse
# permutation inv in the direction of until it hits a "barrier", defined as
# an element greater than it.
d = -1
while True:
y = pi[inv[x] + d] # y is the element next to x in direction d
if x < y:
d = -d # Switch direction
yield False
else:
transpose(pi, inv, x, y)
yield True
def gen_all(n):
# Pad on both sides to allow for a natural stop
pi = [n + 1] + list(range(1, n + 1)) + [n + 1]
inv = pi[:]
# Keep track of directions, all starting negative (move left)
d = [-1] * (n + 2)
x = n # x is the active element
yield pi[1:-1]
while x > 0:
y = pi[inv[x] + d[x]] # y is the element next to x in direction d[x]
if x < y:
d[x] = -d[x] # Switch direction
x -= 1 # Change active element to x - 1
else:
transpose(pi, inv, x, y)
yield pi[1:-1] # New permutation is generated
x = n # Change active element to n
def pruesse_ruskey_product(poset, pi, inv, X, a, b):
Y_ab = pruesse_ruskey_local(poset, pi, inv, a, b)
Y_ba = pruesse_ruskey_local(poset, pi, inv, b, a)
while True:
for result in Y_ab:
if not result:
break
yield result
for result in X:
if not result:
break
if result is SWITCH_SIGN:
transpose(pi, inv, a, b)
Y_ab, Y_ba = Y_ba, Y_ab
yield True
for result in Y_ab:
if not result:
break
yield result
yield False
