Random

class Random

Psuedo random number generator class. Note that all other Random distributions depend upon the uniform distribution, such that reproduction by storage is simplified.

Subclassed by feasst::RandomMT19937

Public Functions

Random(const argtype &args = argtype())

args:

  • seed : Provide an integer to seed the random number generator. If the string “time” is provided, then use the time and date to generate the seed. If no seed is provided, but random numbers are requested, then the time will be used to generate a seed. If the string “default” is provided, then use the default integer included in Random::seed().

void seed_by_time()

Generate seed from time and date.

void seed(const int seed = 1346867550)

Input seed by value for reproducibility.

double uniform()

Return a random real number with a uniform probability distribution between 0 and 1.

int uniform(const int min, const int max)

Return a random integer with a uniform probability distribution betwee min and max.

bool coin_flip()

Randomly return true or false.

double uniform_real(const double min, const double max)

Return random real number with a uniform probability distribution between min and max.

template<class T>
const int index(const std::vector<T> &vector)

Return a random index of a vector.

template<class T>
T *element(std::vector<T> *vector, int *return_index = NULL)

Return a pointer to a random element within a vector.

Parameters

  • return_index: optionally return the index associated with the element.

template<class T>
const T &const_element(const std::vector<T> &vector, int *return_index = NULL)

Return a constant reference to a random element within a vector.

Parameters

  • return_index: optionally return the index associated with the element.

std::string alpha_numeric(const int length = 5)

Return a random alpha numeric string of given length.

Position position_in_cube(const int dimension, const double length = 1)

Return a random position within a cube of side length with the origin at the center.

void position_in_cube(const int dimension, const double length, Position *position)

Optimized version of the above, in that an existing position is modified.

Position position_in_cuboid(const Position &side_length)

Return a random position within a cuboid of side lengths with the origin at the center.

void position_in_cuboid(const Position &side_length, Position *position)

Optimized version of the above, in that an existing position is modified.

void unit_sphere_surface(Position *position)

Random point on the surface of a unit sphere.

void position_in_spherical_shell(const double lower, const double upper, Position *position)

Random point in a spherical shell.

int index_from_cumulative_probability(const std::vector<double> &cumulative)

Given a cumulative probability distribution, return a random integer index from a uniform probability distribution. The cumulative distribution must be monotonically nondecreasing. In addition, it must end with the value of unity.

RotationMatrix rotation(const int dimension, const double max_angle = 180)

Return a random rotation matrix.

Parameters

  • dimension: dimensionality of space

  • max_angle: maximum angle of rotation in degrees.

void rotation(const int dimension, Position *axis, RotationMatrix *rot_mat, const double max_angle = 180)

Same as above, but optimized to reuse existing axis and matrix.

Parameters

  • dimension: dimensionality of space

  • max_angle: maximum angle of rotation in degrees.

virtual double standard_normal()

Return the normal distribution with 0 mean and unit sigma (standard). Use Box-Muller transformation. See: https://mathworld.wolfram.com/Box-MullerTransformation.html

double normal(const double mean, const double stdev)

Same as above, but with a given mean and standard deviation.

double harmonic_bond_length(const double equilibrium_length, const double spring_constant, const int dimension)

Return a randomly selected bond length with harmonic potential of the form: betaU ~ spring_constant*(length - equilibrium_length)**2 The typical 1/2 factor is included in spring_constant. prob(length) ~ length**2 exp(-betaU) dlength as described in Frenkel and Smit, Alg 43, page 578 and Allen and Tildesley, Section G.3. The maximal length is 3 sigma beyond the mean. Only currently implemented for 3 dimensions.

double bond_length(const double equilibrium_length, const double spring_constant, const int exponent, const int dimension)

Same as above, but generalized for arbitrary exponential powers. betaU ~ spring_constant*(length - equilibrium_length)**exponent In this implementation, the maximum bond length is twice the equilibrium. If exponent == 2, use harmonic_bond_length.

double bond_angle(const double equilibrium_angle, const double spring_constant, const int exponent, const int dimension, const double minimum_angle = 0.)

Parameters

  • minimum_angle: Optionally, disallow angles < minimum_angle. The max angle is PI.

Return bond angle selected from probability distribution associated with bending energy, \( \beta U=spring_constant*(t-equil_ang)^{exponent} \) from Frenkel and Smit, page 343, below Equation 13.3.6.

const Cache &cache() const

Return the cache.

void set_cache_to_load(const bool load)

Set Cache to load.

void set_cache_to_unload(const Random &random)

Set Cache to unload.

std::string class_name() const

Serialize.