www.pudn.com > easy_svm.zip > kernel.m, change:2008-02-29,size:1636b


function [K] = kernel(ker,x,y) 
% Calculate kernel function.    
% x: 输入样本,n1×d的矩阵,n1为样本个数,d为样本维数 
% y: 输入样本,n2×d的矩阵,n2为样本个数,d为样本维数 
% ker  核参数(结构体变量) 
% the following fields: 
%   type   - linear :  k(x,y) = x'*y 
%            poly   :  k(x,y) = (x'*y+c)^d 
%            gauss  :  k(x,y) = exp(-0.5*(norm(x-y)/s)^2)   
%                                        % norm命令计算矩阵或向量(x-y)的2-范数 
%            tanh   :  k(x,y) = tanh(g*x'*y+c) 
%   degree - Degree d of polynomial kernel (positive scalar). 
%   offset - Offset c of polynomial and tanh kernel (scalar, negative for tanh). 
%   width  - Width s of Gauss kernel (positive scalar). 
%   gamma  - Slope g of the tanh kernel (positive scalar). 
% ker = struct('type','linear'); 
% ker = struct('type','ploy','degree',d,'offset',c); 
% ker = struct('type','gauss','width',s); 
% ker = struct('type','tanh','gamma',g,'offset',c); 
% K: 输出核参数,n1×n2的矩阵 
%-------------------------------------------------------------% 
switch ker.type 
    case 'linear' 
        K = x*y';         % n*n的矩阵 
    case 'ploy' 
        d = ker.degree; 
        c = ker.offset; 
        K = (x*y'+c).^d; 
    case 'gauss' 
        s = ker.width; 
        rows = size(x,1); 
        cols = size(y,1);    
        tmp = zeros(rows,cols); 
        for i = 1:rows 
            for j = 1:cols 
                tmp(i,j) = norm(x(i,:)-y(j,:)); 
            end 
        end         
        K = exp(-0.5*(tmp/s).^2); 
    case 'tanh' 
        g = ker.gamma; 
        c = ker.offset; 
        K = tanh(g*x*y'+c); 
    otherwise 
        K = 0; 
end