public static double[] linearReg(double[] xData, double[] yData) {
        sameArrayLen(xData, yData);
        double sumX = 0;
        double sumY = 0;
        double prod = 0;
        int nstat = xData.length;
        double[] regCoef = new double[3]; //(intercept, gradient, r2)

        double meanYValue = mean(yData);
        double meanXValue = mean(xData);

        //calculating regression coefficients
        for (int i = 0; i < nstat; i++) {
            sumX += (xData[i] - meanXValue) * (xData[i] - meanXValue);
            sumY += (yData[i] - meanYValue) * (yData[i] - meanYValue);
            prod += (xData[i] - meanXValue) * (yData[i] - meanYValue);
        }
        if (sumX > 0 && sumY > 0) {
            regCoef[1] = prod / sumX;  //gradient
            regCoef[0] = meanYValue - regCoef[1] * meanXValue; //intercept
            regCoef[2] = Math.pow((prod / Math.sqrt(sumX * sumY)), 2); //r2
        }
        return regCoef;
    }