为什么parfor远低于当开销可以忽略不计?

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江民张 2011年9月14日

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这个问题直接联系

//www.tatmou.com/matlabcentral/answers/15797-why-parfor-is-much-slower-than-for-when-the-overhead-is-negligible

我有一个代码如下所示。它与常规的成本660秒

然而,随着parfor,成本超过半个小时。关键是开销可以忽略不计。

= = = = = = = = = = = = = = = = = =

                         清晰的所有;关闭所有;clc;抽搐
                        
                         Nx = 100;纽约= 100;
                        
                         plist = 0.05:0.05:0.95;
                        
                         linked_list = 0(1、长度(plist));
                        
                         num_sample = 20000;
                        
                         matlabpool开3
                        
                         parforsss = 1:长度(plist)
                        
                         瑞士
                        
                         p = plist (sss);
                        
                         numlink = 0;
                        
                         为s10 = 1: num_sample
                        
                         Nx模式=(兰特(纽约)< p);
                        
                         Nx pattern2 = 0(纽约);
                        
                         新= 0 (10000);
                        
                         new2 = 0 (10000);
                        
                         num_new = 0;
                        
                         num_new2 = 0;
                        
                         国旗= 0;
                        
                         发现= 0;
                        
                         s = 0;
                        
                         而(发现= = 0)& & (s < Nx)
                        
                         s = s + 1;
                        
                         如果(模式(1,s) = = 1) & & (pattern2 (1, s) = = 0);
                        
                         国旗=国旗+ 1;
                        
                         pattern2 (s) =国旗;
                        
                         num_new = 1;
                        
                         新(1,1)= s;
                        
                         新(2,1)= 1;
                        
                         num_new2 = 0;
                        
                         而num_new > 0
                        
                         num_new2 = 0;
                        
                         为s1 = 1: num_new
                        
                         x =新(s1);
                        
                         y =新(s1);
                        
                         如果(x > 1) & &(模式(y, x - 1) = = 1) & & (pattern2 (y, x - 1) ~ =国旗)
                        
                         num_new2 = num_new2 + 1;
                        
                         num_new2 new2 (1) = x - 1;
                        
                         num_new2 new2 (2) = y;
                        
                         pattern2 (y、x - 1) =国旗;
                        
                         结束
                        
                         如果(x < Nx) & &(模式(y、x + 1) = = 1) & & (pattern2 (y, x + 1) ~ =国旗)
                        
                         num_new2 = num_new2 + 1;
                        
                         num_new2 new2 (1) = x + 1;
                        
                         num_new2 new2 (2) = y;
                        
                         pattern2 (y、x + 1) =国旗;
                        
                         结束
                        
                         如果(y > 1) & &(模式(y-1 x) = = 1) & & (pattern2 (y-1 x) ~ =标志)
                        
                         num_new2 = num_new2 + 1;
                        
                         num_new2 new2 (1) = x;
                        
                         num_new2 new2 (2) = y-1;
                        
                         pattern2 (y-1 x) =国旗;
                        
                         结束
                        
                         如果(y <纽约)& &(模式(y + 1, x) = = 1) & & (pattern2 (y + 1, x) ~ =国旗)
                        
                         num_new2 = num_new2 + 1;
                        
                         num_new2 new2 (1) = x;
                        
                         num_new2 new2 (2) = y + 1;
                        
                         pattern2 (y + 1, x) =国旗;
                        
                         结束
                        
                         结束
                        
                         num_new = num_new2;
                        
                         新(:,1:num_new) = new2 (:, 1: num_new);
                        
                         如果马克斯(新(2,1:num_new)) = =纽约
                        
                         发现= 1;
                        
                         打破;
                        
                         结束
                        
                         结束
                        
                         结束
                        
                         结束
                        
                         numlink = numlink +发现;
                        
                         结束
                        
                         linked_list (sss) = numlink / num_sample;
                        
                         结束
                        
                         如果matlabpool (“大小”)> 0
                        
                         matlabpool关闭
                        
                         结束
                        
                         情节(linked_list plist,‘*’)
                        
                         toc