code: func (e *Ewma) Init(halfLife time.Duration) *Ewma {
  	*e = Ewma{
  		weightHelper: -math.Ln2 / float64(halfLife.Nanoseconds()),
  	}
  	return e
  }
docs: // Initialize already allocated NewEwma structure
  //
  // halfLife it the time takes for a half charge or half discharge