ema calculation

Swift

    ///  Given an array of prices
    func emas(for range: Int, smoothing: Int = 2) -> [Double?] {
        var ema: Double?
        let multiplier: Double = Double(smoothing) / (Double(range) + 1)
        return (0..<count).map {
            if let last = ema {
                //Sean?
                //ema = last * multiplier + self[$0] * (1 - multiplier)
                //THEbalance
                //ema = (self[$0] - last) * multiplier + last
                // Investopedia
                ema = self[$0] * multiplier + last * (1 - multiplier)
            } else {
                ema = sma(for: range)[$0]
            }
            return ema
        }
    }