如何在一个函数中运行Mersenne Twister？ [英] How to run Mersenne Twister inside a function?

问题描述

我有一小段代码运行Mersenne Twister PRNG，工作原理很好：

  std :: random_device randDev ; 
 std :: mt19937 twister（randDev（））; 
 std :: uniform_int_distribution< int> dist（0,99）; 
 
 for（int i = 0; i <10; i ++）{
 std :: cout< dist（twister） std :: endl; 
} 
  

它输出十个随机数。但是，如果我把完全相同的代码放入一个函数：

  #include< random& 
 
 int getRand（const int& A，const int& B）{
 std :: random_device randDev; 
 std :: mt19937 twister（randDev（））; 
 std :: uniform_int_distribution< int> dist（A，B）; 
 
 return dist（twister）; 
} 
 
 int main（）{
 for（int i = 0; i< 10; i ++）{
 std :: cout< getRand（0,99）<< std :: endl; 
} 
 
 return 0; 
} 
  

它输出相同的数字十次。我刚刚开始使用C ++，所以我不知道是什么原因或如何解决问题。

编辑：问题在于std :: random_device。它可能是在Eclipse C + + IDE（Luna版本）或MinGW 4.8.1中的错误，但无论什么原因，随机数总是相同的。

编辑2：考虑TC的建议和事实，我认为时间（0）将是我使用的一个合适的种子。

<那个时间（0）仍然导致十个相同的数字，这里是最后的代码到目前为止。我知道rand（）是坏的，但它工作。

  #include< iostream> 
 #include< random> 
 
 std :: mt19937 twister（rand（））; 
 
 int getRand（const int& A，const int& B）{
 std :: uniform_int_distribution< int> dist（A，B）; 
 
 return dist（twister）; 
} 
 
 int main（）{
 for（int i = 0; i <10; i ++）{
 std :: cout< getRand（0,99）<< std :: endl; 
} 
 
 return 0; 
} 
  

解决方案

使用？
Visual Studio 2012（不确定2013年）没有一个真正的实现std :: random_device，这意味着它被初始化相同的值每次 - 所以在这种情况下，你会有梅森扭曲器初始化相同

顺便说一句，似乎同样的问题在：

> 为什么我使用std :: random_device与mingw gcc4.8.1 获取相同的序列

所以显然GCC4.8在Windows上也有std :: random_device实现为伪-random。

I have a short piece of code which runs the Mersenne Twister PRNG and it works great:

std::random_device randDev;
std::mt19937 twister(randDev());
std::uniform_int_distribution<int> dist(0,99);

for (int i = 0; i < 10; i++) {
    std::cout << dist(twister) << std::endl;
}

It outputs ten random numbers. However if I put the exact same code into a function:

#include <random>

int getRand(const int& A, const int& B) {
    std::random_device randDev;
    std::mt19937 twister(randDev());
    std::uniform_int_distribution<int> dist(A,B);

    return dist(twister);
}

int main() {
    for (int i = 0; i < 10; i++) {
        std::cout << getRand(0,99) << std::endl;
    }

    return 0;
}

It outputs the same number ten times. I'm just starting out with C++ so I have no idea what causes this or how to go about fixing the problem.

EDIT: The problem lies with std::random_device. It could be a bug in Eclipse C++ IDE (Luna version) or MinGW 4.8.1 but for whatever reason that random number is always the same. I believe time(0) will be a suitable seed for my uses.

EDIT 2: Taking T.C.'s suggestion into account and the fact that time(0) still results in ten of the same number, here's the final code so far. I know rand() is bad but it works.

#include <iostream>
#include <random>

std::mt19937 twister(rand());

int getRand(const int& A, const int& B) {
    std::uniform_int_distribution<int> dist(A,B);

    return dist(twister);
}

int main() {
    for (int i = 0; i < 10; i++) {
        std::cout << getRand(0,99) << std::endl;
    }

    return 0;
}

解决方案

What compiler and OS do you use? Visual Studio 2012 (not sure about 2013) didn't have a real implementation of std::random_device, which means that it was initialized with same value each time - so in such case you would have mersenne twister initialized with same seed each time, thus same result.

And by the way, seems that same question was asked in:

why do I get same sequence for everyrun with std::random_device with mingw gcc4.8.1

so apparently GCC4.8 on Windows also has std::random_device implemented as pseudo-random.

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