使用梅森扭曲器 C++ 生成数字 (0,1)
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Generating number (0,1) using mersenne twister c++
提问by user3508622
I'm working on implementing R code into C++ so that it runs faster, but I am having difficulties implementing mersenne twister. I only wish to generate values between (0,1). Here is what I have that pertains to this question.
我正在努力将 R 代码实现到 C++ 中，以便它运行得更快，但是我在实现 mersenne twiner 时遇到了困难。我只想在 (0,1) 之间生成值。这是我对这个问题的了解。
#include <random>
std::mt19937 generator (123);
std::cout << "Random value: " << generator() << std:: endl;
I tried dividing by RAND_MAX, but that did not produce the values that I was looking for.
我尝试除以RAND_MAX，但这并没有产生我正在寻找的值。
Thanks in advance.
提前致谢。
回答by sbabbi
In C++11 the concepts of "(pseudo) random generator" and "probability distribution" are separated, and for good reasons.
在 C++11 中，“（伪）随机生成器”和“概率分布”的概念是分开的，这是有充分理由的。
What you want can be achieved with the following lines:
您可以通过以下几行实现您想要的：
std::mt19937 generator (123);
std::uniform_real_distribution<double> dis(0.0, 1.0);
double randomRealBetweenZeroAndOne = dis(generator);
If you want to understand why this separation is necessary, and why using a standard division /range manipulation on the output of the generator is a bad idea, watch this video.
如果您想了解为什么这种分离是必要的，以及为什么对生成器的输出使用标准除法/范围操作是个坏主意，请观看此视频。
回答by Mr.C64
You may want to consider code like this:
您可能需要考虑这样的代码：
// For pseudo-random number generators and distributions
#include <random>
...
// Use random_device to generate a seed for Mersenne twister engine.
std::random_device rd{};
// Use Mersenne twister engine to generate pseudo-random numbers.
std::mt19937 engine{rd()};
// "Filter" MT engine's output to generate pseudo-random double values,
// **uniformly distributed** on the closed interval [0, 1].
// (Note that the range is [inclusive, inclusive].)
std::uniform_real_distribution<double> dist{0.0, 1.0};
// Generate pseudo-random number.
double x = dist(engine);
For more details on generating pseudo-random numbers in C++ (including reasons why rand()is notgood), see this video by Stephan T. Lavavej(from Going Native 2013):
有关用C产生伪随机数，更多的细节++（包括原因rand()是没有好），看到这部影片由斯蒂芬T. Lavavej（从融入本土2013）：
回答by galinette
std::mt19937 does not generate between 0 and RAND_MAX like rand(), but between 0 and 2^32-1
std::mt19937 不像 rand() 那样在 0 和 RAND_MAX 之间生成，而是在 0 和 2^32-1 之间生成
And by the way, the class provides min() and max() values!
顺便说一下，该类提供了 min() 和 max() 值！
You need to convert the value to a double, substract min() and divide by max()-min()
您需要将值转换为双精度值，减去 min() 并除以 max()-min()
uint32_t val;
val << generator;
double doubleval = ((double)val - generator::min())/(generator::max()-generator::min());
or (less generic)
或（不太通用）
uint32_t val;
val << generator;
double doubleval = (double)val * (1.0 / std::numeric_limits<std::uint32_t>::max());
