kats/models/nowcasting/feature_extraction.py [171:188]:
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        output_array = np.empty(arr.shape[0], dtype=np.float64)
        output_array[:] = np.NaN

        arr = arr[~np.isnan(arr)]
        n = arr.shape[0]
        ewma = np.empty(n, dtype=np.float64)
        alpha = 2 / float(span + 1)
        w = 1
        ewma_old = arr[0]
        ewma[0] = ewma_old
        for i in range(1, n):
            w += (1 - alpha) ** i
            ewma_old = ewma_old * (1 - alpha) + arr[i]
            ewma[i] = ewma_old / w

        output_subset = ewma[(min_periods - 1) :]
        output_array[-len(output_subset) :] = output_subset
        return output_array
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kats/tsfeatures/tsfeatures.py [1685:1702]:
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        output_array = np.empty(arr.shape[0], dtype=np.float64)
        output_array[:] = np.NaN

        arr = arr[~np.isnan(arr)]
        n = arr.shape[0]
        ewma = np.empty(n, dtype=np.float64)
        alpha = 2 / float(span + 1)
        w = 1
        ewma_old = arr[0]
        ewma[0] = ewma_old
        for i in range(1, n):
            w += (1 - alpha) ** i
            ewma_old = ewma_old * (1 - alpha) + arr[i]
            ewma[i] = ewma_old / w

        output_subset = ewma[(min_periods - 1) :]
        output_array[-len(output_subset) :] = output_subset
        return output_array
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