我想找到旅行商问题的最佳路径，它与顺序算法一起工作正常但是我遇到了并行算法的问题，例如当我按顺序运行时一切正常但是并行时，花了200倍的时间在4核计算机中。
这是我的顺序代码：
#!/usr/local/bin/python
#Traveling Salesman Solution
#Scott Stevenson, Jack Koppenaal, John Costantino
import time, itertools, math
#Get the city file
def getFile():
cityFile = 'in.txt'
try:
f = open(cityFile,'r')
return f
except Exception as e:
print(cityFile + ' could not be opened: ' + str(e))
def find_max():
file = open('in.txt','r')
max = file.read().split()
return max[1]
def initfiles(path):
file = open(path, 'r')
max = file.read().splitlines()
file.close()
file = open(path, 'r')
num = file.read().split()
file.close()
final = list()
final.append(str(num[0] + ' ' + num[1] + ' OK'))
if (num[2] != 'OK'):
print('File has been edited.')
file_write = open(path, 'wt')
for i in range(1, int(num[0]) + 1):
final.append(str(i) + ' ' + str(max[i]))
for line in range(len(final)):
file_write.write(str(final[line]) + '\n')
file_write.close()
#Get distance between 2 cities
#Cities stored as [ident, x, y]
def getDistance(city1, city2):
return math.sqrt((int(city2[1]) - int(city1[1]))**2 + (int(city2[2])-int(city1[2]))**2)
#Get the cities from a specified city file
def getCities(cityFile):
for line in cityFile:
try:
#Lines split by a space char will look like:
#[ident, x-coord, y-coord]
ident = line.split(' ')[0]
x = line.split(' ')[1]
y = line.split(' ')[2].strip('\n')
#print(x,y,ident)
#If the ident is not an int (not a city) skip it otherwise add it
if ident.isdigit():
#Cities are just lists with values (almost a pseudo-class)
city = [int(ident), int(x), int(y)]
cities.append(city)
except:
#The ident was not an int so we skip (pass) it and move on to the next
pass
#A function for bruteforcing the TSP problem based on a list of cities
def bruteForce(cities):
global maxweight
#Tours are also stored as pseudo-class lists
#tour[0] is the path and tour[1] is the weight
#Make a start tour with a weight of infinity so all other tours will be smaller
tour = [[], float("inf")]
permparm = []
#In order to get all permutations we need an array containing the values 1 through n
#These values are the idents of the cities (their 0th element) so we get and add them
for city in cities:
permparm.append(city[0])
#We now generate all permutations of n length from the array containing 1 - n idents
#and loop through them looking for the smallest distance
for perm in list(itertools.permutations(permparm, len(permparm))):
#Get the total weight of the permutation
dist = getWeight(perm)
#Make a new tour to represent the current permutation
thisTour = [perm, dist]
#If the current tour is shorter than the old tour, point the old tour to the new one
if thisTour[1] < tour[1] and thisTour[1]<=int (maxweight):
tour = thisTour
return tour
#Once we have gone through every permutation we have the shortest tour so return it
return tour
#A function to get the total weight of a path
#This function is messy because of an off-by-1 error introduced by the tour file starting at 1 instead of 0
def getWeight(perm):
#Set the initial distance to 0
dist = 0
#We now need to calculate and add the distance between each city in the path from 0 to n
for index in range(len(perm)):
try:
#Pass the 2 cities to the distance formula and add the value to dist
dist += getDistance(cities[perm[index]-1], cities[perm[index+1]-1])
except:
#We don't need to check bounds because the final pass will throw an out-of-bounds
#exception so we just catch it and skip that calculation
pass
#All TSP solutions are cycles so we now have to add the final city back to the initial city to the total dist
#Python has a nifty convention where list[-1] will return the last element, list[-2] will return second to last, etc.
dist += getDistance(cities[perm[-1]-1], cities[perm[0]-1])
#We now have the total distance so return it
#if (int(dist)<=80.0):
return dist
#A function to write the output of a tour to a file in a specified format
def toFile(tour):
loc = input('Enter the location where you would like to save the tour:\n')
fname = cityFile.name
#Index for the last file separator to get ONLY the file name not its path
sep_index = 0
#Linux/OSX files use /'s to separate dirs so get the position of the last one in the name
if '/' in fname:
sep_index = fname.rindex('/')+1
#Windows files use \'s to separate dirs so get the position of the last one in the name
if '\\' in fname:
sep_index = fname.rindex('\\')+1
#Create the header for the output file
header = ('NAME : ' + str(fname[sep_index:-4]) + '.opt.tour\n'
'COMMENT : Optimal tour for ' + str(fname[sep_index:]) + ' (' + str(tour[1]) + ')\n'
'TYPE : Tour\n'
'DIMENSON : ' + str(len(tour[0])) + '\n'
'TOUR_SECTION\n')
#Create the trailer for the output file
trailer = "-1\nEOF\n"
#Create the output file and write the results to it
try:
f = open(loc,'w')
f.write(header)
for city in tour[0]:
f.write(str(city) + '\n')
f.write(trailer)
f.close()
print ('Successfully saved tour data to: ' + loc)
except Exception as e:
print (loc + ' could not be written to: ' + str(e))
#-------------------The actual script begins here-----------------------
cities = []
cityFile = getFile()
maxweight = find_max()
initfiles('in.txt')
#Start the stopwatch
start = time.time()
getCities(cityFile)
opt_tour = bruteForce(cities)
#Stop the stopwatch
finish = time.time()
print ('The optimum tour is: %s (%f)' % (opt_tour[0], opt_tour[1]))
print ('This solution took %0.3f seconds to calculate.' % (finish-start))
我的并行代码：
#!/usr/local/bin/python
import time, itertools, math
from multiprocessing import Pool,Manager
thisTour = None
tour = None
dist = None
totalct = 0
#Get the city file
def getFile():
cityFile = 'in.txt'
try:
f = open(cityFile,'r')
return f
except Exception as e:
print(cityFile + ' could not be opened: ' + str(e))
def find_max():
file = open('in.txt','r')
max = file.read().split()
return max[1]
def initfiles(path):
global totalct
file = open(path, 'r')
max = file.read().splitlines()
totalct = len(max) - 2
file.close()
file = open(path, 'r')
num = file.read().split()
file.close()
final = list()
#print(totalct)
final.append(str(num[0] + ' ' + num[1] + ' OK'))
if (num[2] != 'OK'):
file_write = open(path, 'wt')
for i in range(1, int(num[0]) + 1):
# print(max[i])
final.append(str(i) + ' ' + str(max[i]))
# print(i)
# print(len(final))
for line in range(len(final)):
# print(final[line])
file_write.write(str(final[line]) + '\n')
print('File has been edited.')
file_write.close()
#Get distance between 2 cities
#Cities stored as [ident, x, y]
def getDistance(city1, city2):
return math.sqrt((int(city2[1]) - int(city1[1]))**2 + (int(city2[2])-int(city1[2]))**2)
#Get the cities from a specified city file
def getCities(cityFile):
for line in cityFile:
try:
#Lines split by a space char will look like:
#[ident, x-coord, y-coord]
ident = line.split(' ')[0]
x = line.split(' ')[1]
y = line.split(' ')[2].strip('\n')
#If the ident is not an int (not a city) skip it otherwise add it
if ident.isdigit():
#Cities are just lists with values (almost a pseudo-class)
city = [int(ident), int(x), int(y)]
cities.append(city)
except:
#The ident was not an int so we skip (pass) it and move on to the next
pass
#A function for bruteforcing the TSP problem based on a list of cities
def bruteForce(perm):
global maxweight
global tour
global thisTour
dist = getWeight(perm)
thisTour = [perm, dist]
#If the current tour is shorter than the old tour, point the old tour to the new one
if thisTour[1] < tour[1] and thisTour[1] <= int(maxweight):
tour = thisTour
return tour
#Once we have gone through every permutation we have the shortest tour so return it
return tour
#A function to get the total weight of a path
#This function is messy because of an off-by-1 error introduced by the tour file starting at 1 instead of 0
def getWeight(perm):
#Set the initial distance to 0
dist = 0
#We now need to calculate and add the distance between each city in the path from 0 to n
for index in range(len(perm)):
try:
#Pass the 2 cities to the distance formula and add the value to dist
dist += getDistance(cities[perm[index]-1], cities[perm[index+1]-1])
except:
#We don't need to check bounds because the final pass will throw an out-of-bounds
#exception so we just catch it and skip that calculation
pass
#All TSP solutions are cycles so we now have to add the final city back to the initial city to the total dist
#Python has a nifty convention where list[-1] will return the last element, list[-2] will return second to last, etc.
dist += getDistance(cities[perm[-1] - 1], cities[perm[0] - 1])
#We now have the total distance so return it
return dist
#A function to write the output of a tour to a file in a specified format
def toFile(tour):
loc = input('Enter the location where you would like to save the tour:\n')
fname = cityFile.name
#Index for the last file separator to get ONLY the file name not its path
sep_index = 0
#Linux/OSX files use /'s to separate dirs so get the position of the last one in the name
if '/' in fname:
sep_index = fname.rindex('/')+1
#Windows files use \'s to separate dirs so get the position of the last one in the name
if '\\' in fname:
sep_index = fname.rindex('\\')+1
#Create the header for the output file
header = ('NAME : ' + str(fname[sep_index:-4]) + '.opt.tour\n'
'COMMENT : Optimal tour for ' + str(fname[sep_index:]) + ' (' + str(tour[1]) + ')\n'
'TYPE : Tour\n'
'DIMENSON : ' + str(len(tour[0])) + '\n'
'TOUR_SECTION\n')
#Create the trailer for the output file
trailer = "-1\nEOF\n"
#Create the output file and write the results to it
try:
f = open(loc,'w')
f.write(header)
for city in tour[0]:
f.write(str(city) + '\n')
f.write(trailer)
f.close()
print ('Successfully saved tour data to: ' + loc)
except Exception as e:
print (loc + ' could not be written to: ' + str(e))
#-------------------The actual script begins here-----------------------
def permutations():
allperm = list(itertools.permutations(act, len(act)))
for i in allperm:
allpermlist.append(list(i))
print('permutations compute has been finished.')
return allpermlist
def allct ():
for i in range(1, totalct):
act.append(i)
def init():
global thisTour
global tour
global dist
if __name__ == "__main__":
cities = []
cityFile = getFile()
maxweight = find_max()
initfiles('in.txt')
manager = Manager()
allpermlist = manager.list()
tour = [[], float("inf")]
allpermlist = []
act = []
allct()
permutations()
#Start the stopwatch
start = time.time()
getCities(cityFile)
with Pool(processes=8, initializer=init) as p:
opt_tour = p.map_async(bruteForce, allpermlist, chunksize=2048)
opt_tour.wait()
print(opt_tour.get())
p.close()
#p.join()
finish = time.time()
print('This solution took %0.3f seconds to calculate.' % (finish-start))
我的in.txt：
9 47 OK
1 13 15
2 4 21
3 7 17
4 8 11
5 10 14
6 2 15
7 14 11
8 15 20
9 13 17