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```