Encog.MathUtil.LIBSVM.Kernel.k_function C# (CSharp) Method

        internal static double k_function(svm_node[] x, svm_node[] y, svm_parameter param)
        {
            switch (param.kernel_type)
            {
                case svm_parameter.LINEAR:
                    return dot(x, y);

                case svm_parameter.POLY:
                    return Math.Pow(param.gamma*dot(x, y) + param.coef0, param.degree);

                case svm_parameter.RBF:
                    {
                        double sum = 0;
                        int xlen = x.Length;
                        int ylen = y.Length;
                        int i = 0;
                        int j = 0;
                        while (i < xlen && j < ylen)
                        {
                            if (x[i].index == y[j].index)
                            {
                                double d = x[i++].value_Renamed - y[j++].value_Renamed;
                                sum += d*d;
                            }
                            else if (x[i].index > y[j].index)
                            {
                                sum += y[j].value_Renamed*y[j].value_Renamed;
                                ++j;
                            }
                            else
                            {
                                sum += x[i].value_Renamed*x[i].value_Renamed;
                                ++i;
                            }
                        }

                        while (i < xlen)
                        {
                            sum += x[i].value_Renamed*x[i].value_Renamed;
                            ++i;
                        }

                        while (j < ylen)
                        {
                            sum += y[j].value_Renamed*y[j].value_Renamed;
                            ++j;
                        }

                        return Math.Exp((- param.gamma)*sum);
                    }

                case svm_parameter.SIGMOID:
                    return tanh(param.gamma*dot(x, y) + param.coef0);

                default:
                    return 0; // java
            }
        }
    }