Exemplo n.º 1
0
// Fit sets the parameters of the probability distribution from the
// data samples x with relative weights w.
// If weights is nil, then all the weights are 1.
// If weights is not nil, then the len(weights) must equal len(samples).
//
// Note: Laplace distribution has no FitPrior because it has no sufficient
// statistics.
func (l *Laplace) Fit(samples, weights []float64) {
	if len(samples) != len(weights) {
		panic(badLength)
	}

	if len(samples) == 0 {
		panic(badNoSamples)
	}
	if len(samples) == 1 {
		l.Mu = samples[0]
		l.Scale = 0
		return
	}

	var (
		sortedSamples []float64
		sortedWeights []float64
	)
	if sort.Float64sAreSorted(samples) {
		sortedSamples = samples
		sortedWeights = weights
	} else {
		// Need to copy variables so the input variables aren't effected by the sorting
		sortedSamples = make([]float64, len(samples))
		copy(sortedSamples, samples)
		sortedWeights := make([]float64, len(samples))
		copy(sortedWeights, weights)

		stat.SortWeighted(sortedSamples, sortedWeights)
	}

	// The (weighted) median of the samples is the maximum likelihood estimate
	// of the mean parameter
	// TODO: Rethink quantile type when stat has more options
	l.Mu = stat.Quantile(0.5, stat.Empirical, sortedSamples, sortedWeights)

	sumWeights := floats.Sum(weights)

	// The scale parameter is the average absolute distance
	// between the sample and the mean
	absError := stat.MomentAbout(1, samples, l.Mu, weights)

	l.Scale = absError / sumWeights
}
Exemplo n.º 2
0
// SuffStat computes the sufficient statistics of a set of samples to update
// the distribution. The sufficient statistics are stored in place, and the
// effective number of samples are returned.
//
// The normal distribution has two sufficient statistics, the mean of the samples
// and the standard deviation of the samples.
//
// If weights is nil, the weights are assumed to be 1, otherwise panics if
// len(samples) != len(weights). Panics if len(suffStat) != 2.
func (Normal) SuffStat(samples, weights, suffStat []float64) (nSamples float64) {
	lenSamp := len(samples)
	if len(weights) != 0 && len(samples) != len(weights) {
		panic("dist: slice size mismatch")
	}
	if len(suffStat) != 2 {
		panic("dist: incorrect suffStat length")
	}

	if len(weights) == 0 {
		nSamples = float64(lenSamp)
	} else {
		nSamples = floats.Sum(weights)
	}

	mean := stat.Mean(samples, weights)
	suffStat[0] = mean

	// Use Moment and not StdDev because we want it to be uncorrected
	variance := stat.MomentAbout(2, samples, mean, weights)
	suffStat[1] = math.Sqrt(variance)
	return nSamples
}