C++ Kurtosis with correction for bias (using openCV Mat)

kurtosis.cpp

#include <cmath>

#include <opencv2/core.hpp>

using namespace cv;
using namespace std;

Mat_<float>
ft_kurtosis(cv::Mat_<float> timeseries, int numWindows, int windowLen)
{
    Mat_<float> kurtosis = Mat(numWindows, 1, CV_32F);

    /* calculate mean */
    Mat row_mean;
    reduce(timeseries, row_mean, 1, CV_REDUCE_AVG);

    float m4, m2, avg;
    for (int i = 0; i < numWindows; i++) {
        m4 = m2 = 0;
        avg = row_mean.at<float>(i, 0);
        for (int j = 0; j < windowLen; j++) {
            m4 += pow(timeseries.at<float>(i, j) - avg, 4);
            m2 += pow(timeseries.at<float>(i, j) - avg, 2);
        }

        float n = windowLen;
        if (n > 3 && m2 > 0) {
            kurtosis.at<float>(i, 0) = 1.0 / (n - 2) / (n - 3) 
                * ((pow(n, 2) - 1.0) * ((m4 / n) / pow(m2 / n, 2)) - 3 * pow(n - 1, 2));
        } else {
            kurtosis.at<float>(i, 0) = (m4 / n)
                                / pow(m2 / n, 2) - 3;   
        }
    }

    return kurtosis;
}