1088c261
 tangwang
mv files
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import numpy as np
def create_alias_table(area_ratio):
"""
:param area_ratio: sum(area_ratio)=1
:return: accept,alias
"""
l = len(area_ratio)
area_ratio = [prop * l for prop in area_ratio]
accept, alias = [0] * l, [0] * l
small, large = [], []
for i, prob in enumerate(area_ratio):
if prob < 1.0:
small.append(i)
else:
large.append(i)
while small and large:
small_idx, large_idx = small.pop(), large.pop()
accept[small_idx] = area_ratio[small_idx]
alias[small_idx] = large_idx
area_ratio[large_idx] = area_ratio[large_idx] - \
(1 - area_ratio[small_idx])
if area_ratio[large_idx] < 1.0:
small.append(large_idx)
else:
large.append(large_idx)
while large:
large_idx = large.pop()
accept[large_idx] = 1
while small:
small_idx = small.pop()
accept[small_idx] = 1
return accept, alias
def alias_sample(accept, alias):
"""
:param accept:
:param alias:
:return: sample index
"""
N = len(accept)
i = int(np.random.random()*N)
r = np.random.random()
if r < accept[i]:
return i
else:
return alias[i]
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