Module: FieldTest::Calculations

Defined in:
lib/field_test/calculations.rb

Class Method Summary collapse

Class Method Details

.prob_b_beats_a(alpha_a, beta_a, alpha_b, beta_b) ⇒ Object 



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# File 'lib/field_test/calculations.rb', line 7

def self.prob_b_beats_a(alpha_a, beta_a, alpha_b, beta_b)
  total = 0.0

  # for performance
  logbeta_aa_ba = Math.logbeta(alpha_a, beta_a)
  beta_ba = beta_b + beta_a

  0.upto(alpha_b - 1) do |i|
    total += Math.exp(Math.logbeta(alpha_a + i, beta_ba) -
      Math.log(beta_b + i) - Math.logbeta(1 + i, beta_b) -
      logbeta_aa_ba)
  end

  total
end

.prob_c_beats_a_and_b(alpha_a, beta_a, alpha_b, beta_b, alpha_c, beta_c) ⇒ Object 



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# File 'lib/field_test/calculations.rb', line 23

def self.prob_c_beats_a_and_b(alpha_a, beta_a, alpha_b, beta_b, alpha_c, beta_c)
  total = 0.0

  # for performance
  logbeta_ac_bc = Math.logbeta(alpha_c, beta_c)
  abc = beta_a + beta_b + beta_c
  log_bb_j = []
  logbeta_j_bb = []
  logbeta_ac_i_j = []
  0.upto(alpha_b - 1) do |j|
    log_bb_j[j] = Math.log(beta_b + j)
    logbeta_j_bb[j] = Math.logbeta(1 + j, beta_b)

    0.upto(alpha_a - 1) do |i|
      logbeta_ac_i_j[i + j] ||= Math.logbeta(alpha_c + i + j, abc)
    end
  end

  0.upto(alpha_a - 1) do |i|
    # for performance
    log_ba_i = Math.log(beta_a + i)
    logbeta_i_ba = Math.logbeta(1 + i, beta_a)

    0.upto(alpha_b - 1) do |j|
      total += Math.exp(logbeta_ac_i_j[i + j] -
        log_ba_i - log_bb_j[j] -
        logbeta_i_ba - logbeta_j_bb[j] -
        logbeta_ac_bc)
    end
  end

  1 - prob_b_beats_a(alpha_c, beta_c, alpha_a, beta_a) -
    prob_b_beats_a(alpha_c, beta_c, alpha_b, beta_b) + total
end