/// <summary>
/// Polynomial kernel function.
/// </summary>
///
/// <param name="x">Vector <c>x</c> in input space.</param>
/// <param name="y">Vector <c>y</c> in input space.</param>
/// <returns>Dot product in feature (kernel) space.</returns>
///
public override double Function(double[] x, double[] y)
{
double sum = SparseLinear.Product(x, y) + constant;
return(Math.Pow(sum, Degree));
}
/// <summary>
/// Sigmoid kernel function.
/// </summary>
///
/// <param name="x">Vector <c>x</c> in input space.</param>
/// <param name="y">Vector <c>y</c> in input space.</param>
/// <returns>Dot product in feature (kernel) space.</returns>
///
public override double Function(double[] x, double[] y)
{
double sum = SparseLinear.Product(x, y);
return(System.Math.Tanh(Gamma * sum + Constant));
}