The F-Distribution - Compute and visualize in Java

Hello, I had little time because of my exam, but today I finished the already announced expansion of my program. In addition to the normal distribution and student's t-distribution, the F-distribution is now also included.

Restructuring of source code

The calculation of the gamma function has been moved to a new class for mathematical functions, which will be extended in the future.

public class XMath {

    final static double[] LANCZOSTABLE = {
             1.000000000190015,
            76.18009172947146,
           -86.50532032941677,
            24.01409824083091,
            -1.231739572450155,
             0.1208650973866179e-2,
            -0.5395239384953e-5
        };
        final static double LN_SQRT_2_PI = 0.91893853320467274178;

        /**
         * Callculating Gamma using the Lanczos method
         * 
         * @param x
         * @return logarithm of the Gamma function
         */
        static double ln_gamma_lanczos(double x) {
            
            if (x < 0.5) {
              return Math.log(Math.PI / Math.sin(Math.PI * x)) - ln_gamma_lanczos(1.0 - x);
            }
            
            x = x - 1.0;
            double sum = 0;
            for(int i=1; i<LANCZOSTABLE.length; i++) {
                sum += LANCZOSTABLE[i]/(x+i);
            }
            sum += LANCZOSTABLE[0];
            return ((LN_SQRT_2_PI+Math.log(sum))-x-5.5)+Math.log(x+5.5)*(x+0.5);
            
          }

        public static double gamma(double x) {
            return Math.exp(ln_gamma_lanczos(x));
        }
        
}

New variables

    int m;
    int n;

Changes in the GUI

            labelM = new JLabel();
            labelM.setText("m = ");
            labelM.setBounds(200, 10, 75, 25);
            jPanel.add(labelM);

            textFieldM = new JTextField();
            textFieldM.setText("3");
            textFieldM.setBounds(250, 10, 50, 25);
            jPanel.add(textFieldM);
            
            labelN = new JLabel();
            labelN.setText("n = ");
            labelN.setBounds(300, 10, 75, 25);
            jPanel.add(labelN);

            textFieldN = new JTextField();
            textFieldN.setText("6");
            textFieldN.setBounds(350, 10, 50, 25);
            jPanel.add(textFieldN);

Calculation of the distribution

    double df(double x, int m, int n) {
        if (x<0) {
            return 0.0;
        }
        
        return
            Math.pow(m, m/2.0) * Math.pow(n, n/2.0) *
            XMath.gamma(m/2.0+n/2.0) / (XMath.gamma(m/2.0)*XMath.gamma(n/2.0)) *
            Math.pow(x,m/2.0-1) / Math.pow(m*x+n,(m+n)/2.0);
    }

    public double qf(double alpha, int m, int n) {
        double sum = 0;
        double pos = -1000;
        double stepSize = 0.01;
        while (sum<alpha) {
            sum += df(pos, m, n)*stepSize;
            pos += stepSize;
        }
        return pos;
    }

The chi-square distribution will follow in the next days. And also the simultaneous representation of different distributions is still on the way.