public class KwadraturaGaussa {

   static double[] x = {0, 5, 5, 0};
   static double[] y = {0, 0, 5, 5};
   static double[] waga = {1, 1};
   static double[] punkt = {-0.5773502692, 0.5773502692};
   static double[][][] fksztalt = new double[2][2][4];
   static double[][] poch_ksi = new double[2][4];
   static double[][] poch_ni = new double[2][4];
    static double[][] fun_detj = new double[2][2];
    static double dxdksi ;
    static double dydksi ;
    static double dxdni ;
    static double dydni;

    static void funk() {

        for (int i = 0; i < punkt.length; i++) {

            for (int j = 0; j < punkt.length; j++) {
                fksztalt[j][i][0] = 0.25 * (1.0 - punkt[j]) * (1.0 - punkt[i]);
                fksztalt[j][i][1] = 0.25 * (1.0 + punkt[j]) * (1.0 - punkt[i]);
                fksztalt[j][i][2] = 0.25 * (1.0 + punkt[j]) * (1.0 + punkt[i]);
                fksztalt[j][i][3] = 0.25 * (1.0 - punkt[j]) * (1.0 + punkt[i]);

                poch_ksi[i][0] = -0.25 * (1.0 - punkt[i]);
                poch_ksi[i][1] = 0.25 * (1.0 - punkt[i]);
                poch_ksi[i][2] = 0.25 * (1.0 + punkt[i]);
                poch_ksi[i][3] = -0.25 * (1.0 + punkt[i]);

                poch_ni[j][0] = -0.25 * (1.0 - punkt[j]);
                poch_ni[j][1] = -0.25 * (1.0 + punkt[j]);
                poch_ni[j][2] = 0.25 * (1.0 + punkt[j]);
                poch_ni[j][3] = 0.25 * (1.0 - punkt[j]);
            }
        }

        for (int i = 0; i < 2; i++) {
            for (int j = 0; j < 2; j++) {
                dxdksi = poch_ksi[i][0] * (x[0]) + poch_ksi[i][1] * (x[1]) +
                        poch_ksi[i][2] * (x[2]) + poch_ksi[i][3] * (x[3]);

                dydksi = poch_ksi[i][0] * y[0] + poch_ksi[i][1] * y[1] +
                        poch_ksi[i][2] * y[2] + poch_ksi[i][3] * y[3];

                dxdni = poch_ni[j][0] * (y[0]) + poch_ni[j][1] * (y[1]) +
                        poch_ni[j][2] * (y[2]) + poch_ni[j][3] * (y[3]);


                dydni = poch_ni[j][0] * y[0] + poch_ni[j][1] * y[1] +
                        poch_ni[j][2] * y[2] + poch_ni[j][3] * y[3];

                fun_detj[i][j] = dxdksi*dydni - dxdni*dydksi;


            }
        }
        double powierzchnia = 0.0;
        for (int i = 0; i < punkt.length; i++) {

            for (int j = 0; j < punkt.length; j++) {

                powierzchnia += Math.abs(fun_detj[i][j]);
            }


        }
        System.out.println(powierzchnia);




    }
    public static void main(String[] args)
    {
        KwadraturaGaussa kg = new KwadraturaGaussa();
        funk();
        // Initial Values ---- TO BYLO W INNYM PROJEKCIE
        float x0 = 0;
        float y0 = 1;
        float h = (float) 0.5;


        float x = (float) 3;


    }
}