private void zeileTauschen(int z1, int z2) {
        double[] zeile1 = matrix[z1];
        double[] zeile2 = matrix[z2];
        matrix[z1] = zeile2;
        matrix[z2] = zeile1;
        double tmp = rseite[z1];
        rseite[z1] = rseite[z2];
        rseite[z2] = tmp;
    }