// div3Sigma sets given metric score and average via 3-sigma.
// states that nearly all values (99.7%) lie within the 3 standard deviations
// of the mean in a normal distribution.
func (d *Detector) div3Sigma(m *models.Metric, vals []float64) {
if len(vals) == 0 {
m.Score = 0
m.Average = m.Value
return
}
// Values average and standard deviation.
avg := mathutil.Average(vals)
std := mathutil.StdDev(vals, avg)
// Set metric average
m.Average = avg
// Set metric score
if len(vals) <= int(d.cfg.Detector.LeastCount) { // Number of values not enough
m.Score = 0
return
}
last := m.Value
if std == 0 { // Eadger
switch {
case last == avg:
m.Score = 0
case last > avg:
m.Score = 1
case last < avg:
m.Score = -1
}
return
}
m.Score = (last - avg) / (3 * std) // 3-sigma
}
