client_golang/maths/distributions.go

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2012-05-20 01:59:25 +04:00
// Copyright (c) 2012, Matt T. Proud
// All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// distributions.go provides basic distribution-generating functions that are
// used primarily in testing contexts.
package maths
import (
"math"
)
// Go's standard library does not offer a factorial function.
func Factorial(of int) int64 {
if of <= 0 {
return 1
}
var result int64 = 1
for i := int64(of); i >= 1; i-- {
result *= i
}
return result
}
// Create calculate the value of a probability density for a given binomial
// statistic, where k is the target count of true cases, n is the number of
// subjects, and p is the probability.
func BinomialPDF(k, n int, p float64) float64 {
binomialCoefficient := float64(Factorial(n)) / float64(Factorial(k)*Factorial(n-k))
intermediate := math.Pow(p, float64(k)) * math.Pow(1-p, float64(n-k))
return binomialCoefficient * intermediate
}