morph::Rand*

#include <morph/Random.h>

Header file: morph/Random.h. Test and example code: tests/testRandom tests/testRandString

Summary

High quality random number generation (RNG) is important in many scientific simulation projects. <morph/Random.h> provides a set of random number generation classes. These classes wrap the standard random number generation in the C++ <random> header to give a convenient interface for the programmer. While it is possible to select different pseudo random number generators, the classes all default to the very acceptable mt19937 Mersenne Twister algorithm (using the 32 bit version for RandUniform/RandPoisson and the 64 bit version for RandNormal and RandLogNormal).

Intervals

This page uses the common mathematical notation for intervals:

[a,b) for a semi-closed interval which includes values from and including a up to, but not including b.
[a,b] for a closed interval which includes both a and b in the interval.

morph::RandUniform

Random number generation from a uniform distribution. Any possible value in the interval is equally likely to be returned. The RandUniform class is templated and has integer and floating point specializations:

namespace morph {
    template <typename T = float, typename E = std::mt19937, bool = std::is_integral<std::decay_t<T>>::value>
    class RandUniform {};
    // Both integer and floating point specializations are implemented

T is the type for the generated random numbers and E is the generator algorithm/engine.

Simplest usage

// Floating point RandUniform defaults to the semi-closed interval [0,1)
morph::RandUniform<float> rng1; // Generate random numbers in float type output in interval [0,1)
float f = rng1.get();           // 0 <= f < 1

// By default, an integer RandUniform provides a number from the closed interval [min, max] for the type
morph::RandUniform<unsigned short> rng2;
unsigned short us = rng2.get(); // 0 <= us <= 65535
// Find the end points of the RNG interval with min() and max():
std::cout << "Integer RNG generates numbers in range " << rng2.min() << " to " << rng2.max() << std::endl;

Setting the interval

You can choose an interval over which random numbers should be generated in the constructor

// Create a generator of integer values in interval [0,10]. The interval type should match
// the RandUniform template type (unsigned int here)
morph::RandUniform<unsigned int> rng (0, 10);

// Create a floating point RNG for the interval [-100, 100)
morph::RandUniform<double> rng (-100.0, 100.0);

Using a fixed seed

To use a fixed seed with the default interval, use a single unsigned int argument to the constructor:

morph::RandUniform<int> rng (2303); // The first .get() should always return the same number now

To use a fixed seed with a custom interval, it’s the third argument:

// Declaration
RandUniform (T a, T b, unsigned int _seed);

// In use:
morph::RandUniform<int> rng (0, 100, 2303); // Interval [0,100], seed = 2303

Getting arrays of randomly generated values

If you need to obtain a large number of randomly generated values, it is most efficient to get these into an array, rather than using RandUniform::get()` repeatedly.

morph::RandUniform<double> rng (0.0, 10.0);

// One overload returns std::vector of results
std::vector<double> randoms_in_vector = rng.get (100); // Return a vector with 100 random numbers

// Another places values into an existing std::array
std::array<double, 100> randoms_in_array;
rng.get (randoms_in_array);

Changing the engine

By default the 32 bit mt19937 Mersenne Twister algorithm is used in RandUniform. To select a different engine, specify it as a second template parameter.

morph::RandUniform<float, std::mt19937_64> rng1;  // Use the 64 bit version of mt19937
morph::RandUniform<float, std::minstd_rand> rng2; // Use the linear congruential engine

There are some notes about the different engines that you can use in the comments in morph/Random.h. You can also consult C++ reference material.

One-line RandUniform calls

This is a way to use RandUniform in your program with a single line of code. It creates one singleton class that manages the memory used by the RandUniform<float> object and one for RandUniform<double> and allows you to retrieve random values with morph::randSingle and morph::randDouble function calls:

#include <morph/rng.h>
int main() {
    float rnum_single = morph::randSingle();  // single precision or...
    double rnum_double = morph::randDouble(); // double.
    return 0;
}

To enable only randSingle use #include <morph/rngs.h> and to enable only randDouble, use #include <morph/rngd.h>. There is no equivalent for RandNormal or any of the other Rand* classes, but it would not be difficult to copy and adapt rng.h if you need this.

morph::RandNormal and morph::RandLogNormal

Two C++ classes to generate values from either a normal (Gaussian) distribution or a log-normal distribution.

All the examples here show RandNormal, but you can substitute RandLogNormal if you want the log-normal distribution to generate your values.

namespace morph {
    template <typename T = double, typename E = std::mt19937_64>
    class RandNormal { // or class RandLogNormal

T is the type for the generated random numbers and E is the generator algorithm/engine.

Simplest usage

To generate values from a normal distribution with mean 0 and standard deviation 1, create the a default RandNormal object:

morph::RandNormal<float> rng;
rng.get(); // Getters are the same across the Rand* classes

Specifying the normal distribution parameters

The mean and standard deviation can be specified in the constructor:

morph::RandNormal<double> rng (1.0, 2.0); // Mean 1, standard deviation 2.

Using a fixed seed

To use a fixed seed with the default interval, use a single unsigned int argument to the constructor:

morph::RandNormal<double> rng (2303); // The first .get() should always return the same number now

To use a fixed seed with a custom interval, it’s the third argument:

// Declaration
RandNormal (T a, T b, unsigned int _seed);
// In use:
morph::RandNormal<float> rng (2.0f, 3.0f, 2303); // mean 2, std 3, seed = 2303

Getters

The get() function overloads are the same in all the Rand* classes, so you can:

T value = rng.get();
// or
std::vector<T> values = rng.get (num);
// or
std::array<T, N> avals;
rng.get (avals);

morph::RandPoisson

A C++ classes to generate values from a normal Poisson distribution.

namespace morph {
    template <typename T = int, typename E = std::mt19937>
    class RandPoisson

T is the integral type for the generated random numbers and E is the generator algorithm/engine.

Simplest usage

To generate values from a Poisson distribution with mean 0, create the a default object:

morph::RandPoisson<int> rng;
rng.get();

Specifying the distribution mean

The mean can be specified in the constructor:

morph::RandPoisson<int> rng (3); // Mean 3

Using a fixed seed

To use a fixed seed with the default interval, use a single unsigned int argument to the constructor:

morph::RandPoisson<int> rng (2303); // The first .get() should always return the same number now

To use a fixed seed with a custom mean, it’s the second argument:

// Declaration
RandPoisson (T mean, unsigned int _seed);
// In use:
morph::RandPoisson<int> rng (4, 2303); // mean 4, seed = 2303

Getters

The get() function overloads are the same as for RandUniform, RandNormal and RandLogNormal.

morph::RandString

The RandString class is a little different from the other Rand* classes because it uses a morph::RandUniform member to help it generate character strings. It allows you to generate random characters from different character groups such as morph::CharGroup::AlphaNumeric or morph::CharGroup::Decimal. It is a non-templated class:

namespace morph {
    class RandString

Simplest usage

To generate 8 HexLowerCase characters:

morph::RandString string_gen; // Default string length 8, default char group HexLowerCase.
std::string randchars = string_gen.get();

You can get any length of string. For the example above, to get another 10 HexLowerCase characters:

std::string morechars = string_gen.get (10); // updates RandString::length to 10 before getting chars

You can also change the character group at runtime:

string_gen.setCharGroup (morph::CharGroup::AlphaNumeric);

Constructors

RandString();                  // Default, length set to 8, char group set to HexLowerCase
RandString(const size_t l)     // Construct with length set to l
RandString(const size_t l, const morph::CharGroup& _cg) // Length l, character group _cg

The list of possible character groups is given by the CharGroup declaration:

namespace morph {
   enum class CharGroup
    {
        AlphaNumeric,          // 0-9A-Za-z                   62 chars
        Alpha,                 // A-Za-z                      52 chars
        AlphaNumericUpperCase, // 0123456789ABCDEF... ...XYZ  36 chars
        AlphaNumericLowerCase, // 0123456789abcdef... ...xyz  36 chars
        AlphaUpperCase,        // A-Z                         26 chars
        AlphaLowerCase,        // a-z                         26 chars
        HexUpperCase,          // 0123456789ABCDEF            16 chars
        HexLowerCase,          // 0123456789abcdef            16 chars
        Decimal,               // 0123456789                  10 chars
        BinaryTF,              // TF                           2 chars
        Binary                 // 01                           2 chars
    };
}