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module Distribution
module Gamma
module GSL_
class << self
def pdf(x, a, b)
GSL::Ran.gamma_pdf(x.to_f, a.to_f, b.to_f)
end
# Chi-square cumulative distribution function (cdf).
#
# Returns the integral of Chi-squared distribution
# with k degrees of freedom over [0, x]
#
def cdf(x, a, b)
GSL::Cdf.gamma_P(x.to_f, a.to_f, b.to_f)
end
# Return the P-value of the corresponding integral with
# k degrees of freedom
def quantile(pr, a, b)
GSL::Cdf.gamma_Pinv(pr.to_f, a.to_f, b.to_f)
end
alias_method :p_value, :quantile
end
end
end
end
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