Class: SimpleRandom

Inherits:
Object
  • Object
show all
Defined in:
lib/simple-random/simple_random.rb

Direct Known Subclasses

MultiThreadedSimpleRandom

Defined Under Namespace

Classes: InvalidSeedArgument

Constant Summary collapse

I_32_BIT = 
4294967296
F_32_BIT = 
4294967296.0
DEFAULT_SEEDS = 
[521288629, 362436069]

Instance Method Summary collapse

Constructor Details

#initialize(*args) ⇒ SimpleRandom

Returns a new instance of SimpleRandom.



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# File 'lib/simple-random/simple_random.rb', line 8

def initialize(*args)
  if args.empty?
    set_seed(*DEFAULT_SEEDS)
  else
    set_seed(*args)
  end
end

Instance Method Details

#beta(a, b) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 102

def beta(a, b)
  fail ArgumentError, "Parameters must be strictly positive" unless a > 0 && b > 0
  u = gamma(a, 1)
  v = gamma(b, 1)
  u / (u + v)
end

#cauchy(median, scale) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 115

def cauchy(median, scale)
  fail ArgumentError, 'Scale must be positive' unless scale > 0

  median + scale * Math.tan(Math::PI * (uniform - 0.5))
end

#chi_square(degrees_of_freedom) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 94

def chi_square(degrees_of_freedom)
  gamma(0.5 * degrees_of_freedom, 2.0)
end

#dirichlet(*parameters) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 139

def dirichlet(*parameters)
  sample = parameters.map { |a| gamma(a, 1) }
  sum = sample.inject(0.0) { |sum, g| sum + g }
  sample.map { |g| g / sum }
end

#exponential(mean = 1) ⇒ Object

Get exponential random sample with specified mean



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# File 'lib/simple-random/simple_random.rb', line 47

def exponential(mean = 1)
  fail ArgumentError, "Mean must be strictly positive" unless mean > 0

  -1.0 * mean * Math.log(uniform)
end

#gamma(shape, scale) ⇒ Object

Implementation based on “A Simple Method for Generating Gamma Variables” by George Marsaglia and Wai Wan Tsang. ACM Transactions on Mathematical Software Vol 26, No 3, September 2000, pages 363-372.



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# File 'lib/simple-random/simple_random.rb', line 71

def gamma(shape, scale)
  fail ArgumentError, 'Shape must be strictly positive' unless shape > 0
  return scale * gamma(shape + 1.0, 1.0) * uniform ** -shape if shape < 1

  d = shape - 1 / 3.0
  c = (9 * d) ** -0.5

  begin
    z = normal

    condition1 = z > (-1.0 / c)
    condition2 = false

    if condition1
      u = uniform
      v = (1 + c * z) ** 3
      condition2 = Math.log(u) < (0.5 * (z ** 2) + d * (1.0 - v + Math.log(v)))
    end
  end while !condition2

  scale * d * v
end

#inverse_gamma(shape, scale) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 98

def inverse_gamma(shape, scale)
  1.0 / gamma(shape, 1.0 / scale)
end

#laplace(mean, scale) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 127

def laplace(mean, scale)
  u_1 = uniform(-0.5, 0.5)
  u_2 = uniform

  sign = u_1 / u_1.abs
  mean + sign * scale * Math.log(1 - u_2)
end

#log_normal(mu, sigma) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 135

def log_normal(mu, sigma)
  Math.exp(normal(mu, sigma))
end

#normal(mean = 0.0, standard_deviation = 1.0) ⇒ Object

Sample normal distribution with given mean and standard deviation



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# File 'lib/simple-random/simple_random.rb', line 40

def normal(mean = 0.0, standard_deviation = 1.0)
  fail ArgumentError, 'Standard deviation must be strictly positive' unless standard_deviation > 0

  mean + standard_deviation * ((-2.0 * Math.log(uniform)) ** 0.5) * Math.sin(2.0 * Math::PI * uniform)
end

#seeds ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 28

def seeds
  [@m_w, @m_z]
end

#seeds=(value) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 24

def seeds=(value)
  set_seed(*[value].flatten.compact)
end

#set_seed(*args) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 16

def set_seed(*args)
  validate_seeds!(*args)

  @m_w, @m_z = determine_seeds(*args)

  ensure_32bit_seeds!
end

#student_t(degrees_of_freedom) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 121

def student_t(degrees_of_freedom)
  fail ArgumentError, 'Degrees of freedom must be strictly positive' unless degrees_of_freedom > 0

  normal / ((chi_square(degrees_of_freedom) / degrees_of_freedom) ** 0.5)
end

#triangular(lower, mode, upper) ⇒ Object

Get triangular random sample with specified lower limit, mode, upper limit



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# File 'lib/simple-random/simple_random.rb', line 54

def triangular(lower, mode, upper)
  fail ArgumentError, 'Upper bound must be greater than lower bound.' unless lower < upper
  fail ArgumentError, 'Mode must lie between the upper and lower limits' if mode > upper || mode < lower

  r = (upper - lower).to_f
  u = uniform

  if u < ((mode - lower) / r)
    lower + Math.sqrt(u * r * (mode - lower))
  else
    upper - Math.sqrt((1.0 - u) * r * (upper - mode))
  end
end

#uniform(lower = 0, upper = 1) ⇒ Object

Produce a uniform random sample from the open interval (lower, upper).



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# File 'lib/simple-random/simple_random.rb', line 33

def uniform(lower = 0, upper = 1)
  fail ArgumentError, 'Upper bound must be greater than lower bound.' unless lower < upper

  ((get_unsigned_int + 1) * (upper - lower) / F_32_BIT) + lower
end

#weibull(shape, scale) ⇒ Object 



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# File 'lib/simple-random/simple_random.rb', line 109

def weibull(shape, scale)
  fail ArgumentError, 'Shape and scale must be positive' unless shape > 0 && scale > 0

  scale * ((-Math.log(uniform)) ** (1.0 / shape))
end