我正在研究一个简单的蒙特卡罗模拟脚本,稍后我会扩展它用于更大的项目。该脚本是一个基本的爬虫,试图从网格中的A点到达B点。点A的坐标是(1,1)(这是左上角),点B的坐标是(n,n)(这是右下角,n是网格的大小)。
爬虫开始移动后,有四个选项,可以向左,向右,向上或向下(不允许对角线移动)。如果这四个选项中的任何一个满足以下条件:
新点将在剩余的有效选项中随机选择(据我所知,Python使用Mersenne Twister算法来选择随机数)。
我想运行模拟1,000,000次(以下代码仅运行100次),每次迭代都应该终止:
我以为我正确地实现了算法,但显然有些不对劲。无论我运行多少次模拟(100或1,000,000),我只能获得一个成功的事件,爬虫可以设法到达终点,其余的尝试(99或999,999)都不成功。
我打赌我错过了一些简单的东西,但由于某种原因看不到它。有什么想法吗?
非常感谢!
编辑:文中的一些拼写错误已得到纠正。
import random
i = 1 # initial coordinate top left corner
j = 1 # initial coordinate top left corner
k = 0 # counter for number of simulations
n = 3 # Grid size
foundRoute = 0 # counter for number of cases where the final point is reached
gotStuck = 0 # counter for number of cases where no valid options found
coordList = [[i, j]]
while k < 100:
while True:
validOptions = []
opt1 = [i - 1, j]
opt2 = [i, j + 1]
opt3 = [i + 1, j]
opt4 = [i, j - 1]
# Check 4 possible options out of bound and re-visited coordinates are
# discarded:
if opt1[0] != 0 and opt1[0] <= n and opt1[1] != 0 and opt1[1] <= n:
if not opt1 in coordList:
validOptions.append(opt1)
if opt2[0] != 0 and opt2[0] <= n and opt2[1] != 0 and opt2[1] <= n:
if not opt2 in coordList:
validOptions.append(opt2)
if opt3[0] != 0 and opt3[0] <= n and opt3[1] != 0 and opt3[1] <= n:
if not opt3 in coordList:
validOptions.append(opt3)
if opt4[0] != 0 and opt4[0] <= n and opt4[1] != 0 and opt4[1] <= n:
if not opt4 in coordList:
validOptions.append(opt4)
# Break loop if there are no valid options
if len(validOptions) == 0:
gotStuck = gotStuck + 1
break
# Get random coordinate among current valid options
newCoord = random.choice(validOptions)
# Append new coordinate to the list of grid points visited (to be used
# for checks)
coordList.append(newCoord)
# Break loop if lower right corner of the grid is reached
if newCoord == [n, n]:
foundRoute = foundRoute + 1
break
# If the loop is not broken, assign new coordinates
i = newCoord[0]
j = newCoord[1]
k = k + 1
print 'Route found %i times' % foundRoute
print 'Route not found %i times' % gotStuck
答案 0 :(得分:3)
您的问题是,您永远不会清理您访问过的地点。更改突破内部while
循环的块看起来像这样:
if len(validOptions) == 0:
gotStuck = gotStuck + 1
coordList = [[1,1]]
i,j = (1,1)
break
您还需要在成功的地方更改块:
if newCoord == [n, n]:
foundRoute = foundRoute + 1
coordList = [[1,1]]
i,j = (1,1)
break
或者,您可以简单地将此代码放在内部while
循环之前。然后代码的开头如下:
k = 0 # counter for number of simulations
n = 3 # Grid size
foundRoute = 0 # counter for number of cases where the final point is reached
gotStuck = 0 # counter for number of cases where no valid options found
while k < 100:
i,j = (1,1)
coordList = [[i,j]]
while True:
#Everything else