fixed dependencies

vendor/gonum.org/v1/gonum/stat/distuv/logistic.go

@@ -0,0 +1,98 @@
+// Copyright ©2021 The Gonum Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package distuv
+
+import (
+	"math"
+)
+
+// Logistic implements the Logistic distribution, a two-parameter distribution with support on the real axis.
+// Its cumulative distribution function is the logistic function.
+//
+// General form of probability density function for Logistic distribution is
+//
+//	E(x) / (s * (1 + E(x))^2)
+//	where E(x) = exp(-(x-μ)/s)
+//
+// For more information, see https://en.wikipedia.org/wiki/Logistic_distribution.
+type Logistic struct {
+	Mu float64 // Mean value
+	S  float64 // Scale parameter proportional to standard deviation
+}
+
+// CDF computes the value of the cumulative density function at x.
+func (l Logistic) CDF(x float64) float64 {
+	return 1 / (1 + math.Exp(-(x-l.Mu)/l.S))
+}
+
+// ExKurtosis returns the excess kurtosis of the distribution.
+func (l Logistic) ExKurtosis() float64 {
+	return 6.0 / 5.0
+}
+
+// LogProb computes the natural logarithm of the value of the probability
+// density function at x.
+func (l Logistic) LogProb(x float64) float64 {
+	return x - 2*math.Log(math.Exp(x)+1)
+}
+
+// Mean returns the mean of the probability distribution.
+func (l Logistic) Mean() float64 {
+	return l.Mu
+}
+
+// Mode returns the mode of the distribution.
+//
+// It is same as Mean for Logistic distribution.
+func (l Logistic) Mode() float64 {
+	return l.Mu
+}
+
+// Median returns the median of the distribution.
+//
+// It is same as Mean for Logistic distribution.
+func (l Logistic) Median() float64 {
+	return l.Mu
+}
+
+// NumParameters returns the number of parameters in the distribution.
+//
+// Always returns 2.
+func (l Logistic) NumParameters() int {
+	return 2
+}
+
+// Prob computes the value of the probability density function at x.
+func (l Logistic) Prob(x float64) float64 {
+	E := math.Exp(-(x - l.Mu) / l.S)
+	return E / (l.S * math.Pow(1+E, 2))
+}
+
+// Quantile returns the inverse of the cumulative distribution function.
+func (l Logistic) Quantile(p float64) float64 {
+	return l.Mu + l.S*math.Log(p/(1-p))
+}
+
+// Skewness returns the skewness of the distribution.
+//
+// Always 0 for Logistic distribution.
+func (l Logistic) Skewness() float64 {
+	return 0
+}
+
+// StdDev returns the standard deviation of the probability distribution.
+func (l Logistic) StdDev() float64 {
+	return l.S * math.Pi / sqrt3
+}
+
+// Survival returns the survival function (complementary CDF) at x.
+func (l Logistic) Survival(x float64) float64 {
+	return 1 - l.CDF(x)
+}
+
+// Variance returns the variance of the probability distribution.
+func (l Logistic) Variance() float64 {
+	return l.S * l.S * math.Pi * math.Pi / 3
+}