将“最小到最大"均匀的实际分布会产生Inf，-Inf或NaN吗? [英] Will "min to max" uniform real distribution produce Inf,-Inf, or NaN?

问题描述

如果我要通过以下方式生成浮点值:

template <typename T>
T RandomFromRange(T low, T high){
    std::random_device random_device;
    std::mt19937 engine{random_device()};
    std::uniform_real_distribution<T> dist(low, high);
    return dist(engine);
}

template <typename T>
T GetRandom(){
    return RandomFromRange
    (std::numeric_limits<T>::min(),std::numeric_limits<T>::max());
}

//produce floating point values:
auto num1 = GetRandom<float>();
auto num2 = GetRandom<float>();
auto num3 = GetRandom<float>();
//...

我是否有可能找回NaN，Inf或-Inf?

解决方案

让我们考虑一下std::uniform_real_distribution生成的内容.

产生随机浮点值i，它们均匀分布在间隔[a，b)

因此，它介于std::numeric_limits<foat>::min()和std::numeric_limits<float>::max()之间，包括前者，但不包括后者.这些限制返回什么值?它们分别返回FLT_MIN和FLT_MAX.好吧，那是什么?

最小归一化的正浮点数

最大可表示的有限浮点数

由于{positive，negative} infinity和NaN都不在有限数范围内，因此不会生成它们.

如克里斯托弗·奥里克斯(Christopher Oicles)所指出的那样，请注意，FLT_MIN以及由此扩展的std::numeric_limits<foat>::min()是最小的正可表示值.

如Chris Dodd所指出的，如果 [min, max)的范围超过std::numeric_limits<float>::max()，那么您将获得未定义的行为，在这种情况下，包括生成无穷大在内的任何输出都是可能的. /p>

If I were to produce floating point values in the following way:

template <typename T>
T RandomFromRange(T low, T high){
    std::random_device random_device;
    std::mt19937 engine{random_device()};
    std::uniform_real_distribution<T> dist(low, high);
    return dist(engine);
}

template <typename T>
T GetRandom(){
    return RandomFromRange
    (std::numeric_limits<T>::min(),std::numeric_limits<T>::max());
}

//produce floating point values:
auto num1 = GetRandom<float>();
auto num2 = GetRandom<float>();
auto num3 = GetRandom<float>();
//...

Is it possible that I will ever get back a NaN, Inf, or -Inf?

解决方案

Let's consider what std::uniform_real_distribution generates.

Produces random floating-point values i, uniformly distributed on the interval [a, b)

So, that's between std::numeric_limits<foat>::min() and std::numeric_limits<float>::max(), including former, but excluding latter. What values do those limits return? They return FLT_MIN and FLT_MAX respectively. Well, what are those?

minimum normalized positive floating-point number

maximum representable finite floating-point number

Since neither {positive,negative} infinity, nor NaN is within the range of finite numbers, no they're not generated.

As pointed out by Christopher Oicles, pay attention that FLT_MIN and by extension, std::numeric_limits<foat>::min() is the smallest positive representable value.

As pointed out by Chris Dodd, if the range of [min, max) exceeds std::numeric_limits<float>::max(), then you would get undefined behaviour and in that case any output, including generating infinity would be possible.

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