smile.math.rbf.RadialBasisFunction Maven / Gradle / Ivy
/******************************************************************************
* Confidential Proprietary *
* (c) Copyright Haifeng Li 2011, All Rights Reserved *
******************************************************************************/
package smile.math.rbf;
import smile.math.Function;
/**
* A radial basis function (RBF) is a real-valued function whose value depends
* only on the distance from the origin, so that φ(x)=φ(||x||); or
* alternatively on the distance from some other point c, called a center, so
* that φ(x,c)=φ(||x-c||). Any function φ that satisfies the
* property is a radial function. The norm is usually Euclidean distance,
* although other distance functions are also possible. For example by
* using probability metric it is for some radial functions possible
* to avoid problems with ill conditioning of the matrix solved to
* determine coefficients wi (see below), since the ||x|| is always
* greater than zero.
*
* Sums of radial basis functions are typically used to approximate given
* functions:
*
* y(x) = Σ wi φ(||x-ci||)
*
* where the approximating function y(x) is represented as a sum of N radial
* basis functions, each associated with a different center ci, and weighted
* by an appropriate coefficient wi. The weights wi can
* be estimated using the matrix methods of linear least squares, because
* the approximating function is linear in the weights.
*
* This approximation process can also be interpreted as a simple kind of neural
* network and has been particularly used in time series prediction and control
* of nonlinear systems exhibiting sufficiently simple chaotic behavior,
* 3D reconstruction in computer graphics (for example, hierarchical RBF).
*
* @author Haifeng Li
*/
public interface RadialBasisFunction extends Function {
}