std::normal_distribution - cppreference.com (original) (raw)
| | | | | ----------------------------------------------------------------- | | ------------- | | template< class RealType = double > class normal_distribution; | | (since C++11) |
Generates random numbers according to the Normal (or Gaussian) random number distribution. It is defined as:
\(\small{f(x;\mu,\sigma)}=\frac{1}{\sigma\sqrt{2\pi} }\exp{(-\frac{1}{2}{(\frac{x-\mu}{\sigma})}^2)}\)f(x; μ,σ) = exp⎛
⎜
⎝ ⎛
⎜
⎝⎞
⎟
⎠2
⎞
⎟
⎠
Here \(\small\mu\)μ is the Mean and \(\small\sigma\)σ is the Standard deviation (stddev).
std::normal_distribution satisfies all requirements of RandomNumberDistribution.
Contents
- 1 Template parameters
- 2 Member types
- 3 Member functions
- 4 Non-member functions
- 5 Example
- 6 External links
[edit] Template parameters
| RealType | - | The result type generated by the generator. The effect is undefined if this is not one of float, double, or long double. |
|---|
[edit] Member types
| Member type | Definition |
|---|---|
| result_type (C++11) | RealType |
| param_type (C++11) | the type of the parameter set, see RandomNumberDistribution. |
[edit] Member functions
| (constructor)(C++11) | constructs new distribution (public member function) [edit] |
|---|---|
| reset(C++11) | resets the internal state of the distribution (public member function) [edit] |
| Generation | |
| operator()(C++11) | generates the next random number in the distribution (public member function) [edit] |
| Characteristics | |
| meanstddev(C++11) | returns the distribution parameters (public member function) [edit] |
| param(C++11) | gets or sets the distribution parameter object (public member function) [edit] |
| min(C++11) | returns the minimum potentially generated value (public member function) [edit] |
| max(C++11) | returns the maximum potentially generated value (public member function) [edit] |
[edit] Non-member functions
[edit] Example
#include #include #include #include #include #include int main() { std::random_device rd{}; std::mt19937 gen{rd()}; // Values near the mean are the most likely. Standard deviation // affects the dispersion of generated values from the mean. std::normal_distribution d{5.0, 2.0}; // Draw a sample from the normal distribution and round it to an integer. auto random_int = [&d, &gen]{ return std::lround(d(gen)); }; std::map<long, unsigned> histogram{}; for (auto n{10000}; n; --n) ++histogram[random_int()]; for (const auto [k, v] : histogram) std::cout << std::setw(2) << k << ' ' << std::string(v / 200, '*') << '\n'; }
Possible output:
-1 0 1 * 2 *** 3 ***** 4 ******** 5 ********* 6 ********* 7 ****** 8 *** 9 * 10 11