import numpy as np
import random
import copy
'''
维特比解码和beam search
'''
class Fence:
def __init__(self, n, h):
self.width = n
self.height = h
#用行列组成的list代表一个节点，每两个相邻的列的节点之间可以计算距离
#e.g:node1 = [2,1] node2 = [3, 2]
#为两个节点给一个固定的路径分值
def score(self, node1, node2):
if node1 == "start":
return (node2[0] + node2[1] + 1) / (node2[0] * node2[1] + 1)
assert node1[1] + 1 == node2[1] #保证两个节点处于相邻列
mod = (node1[0] + node1[1] + node2[0] + node2[1]) % 3 + 1
mod /= node1[0] * 4 + node1[1] * 3 + node2[0] * 2 + node2[1] * 1
return mod
class Path:
#定义一个路径
#路径由数个节点组成，并且具有一个路径总分
def __init__(self):
self.nodes = ["start"]
self.score = 0
def __len__(self):
return len(self.nodes)
def beam_search(fence, beam_size):
width = fence.width
height = fence.height
starter = Path()
beam_buffer = [starter]
new_beam_buffer = []
while True:
for path in beam_buffer:
path_length = len(path) - 1
for h in range(height):
node = [h, path_length]
new_path = copy.deepcopy(path)
new_path.score += fence.score(path.nodes[-1], node)
new_path.nodes.append(node)
new_beam_buffer.append(new_path)
new_beam_buffer = sorted(new_beam_buffer, key=lambda x:x.score)
beam_buffer = new_beam_buffer[:beam_size]
new_beam_buffer = []
if len(beam_buffer[0]) == width + 1:
break
return beam_buffer
def viterbi(fence):
width = fence.width
height = fence.height
starter = Path()
beam_buffer = [starter]
new_beam_buffer = []
while True:
for h in range(height):
path_length = len(beam_buffer[0]) - 1
node = [h, path_length]
node_path = []
for path in beam_buffer:
new_path = copy.deepcopy(path)
new_path.score += fence.score(path.nodes[-1], node)
new_path.nodes.append(node)
node_path.append(new_path)
node_path = sorted(node_path, key=lambda x:x.score)
new_beam_buffer.append(node_path[0])
beam_buffer = new_beam_buffer
new_beam_buffer = []
if len(beam_buffer[0]) == width + 1:
break
return sorted(beam_buffer, key=lambda x:x.score)
width = 6
height = 4
fence = Fence(width, height)
# print(fence.score([1,2], [3,3]))
beam_size = 1
res = beam_search(fence, beam_size)
for i in range(beam_size):
print(res[i].nodes, res[i].score)
print("-----------")
res = viterbi(fence)
for path in res:
print(path.nodes, path.score)
