kernel.m

支持向量机工具箱备份,本程序易看,实用!

function [K] = kernel(ker,x,y)
% Calculate kernel function.   
%
% x: 输入样本,d×n1的矩阵,n1为样本个数,d为样本维数
% y: 输入样本,d×n2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)
%            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).
%
%struct()在matlab中是用来建立结构体数组的。通常有两种用法： 
%s = struct('field1',{},'field2',{},...) 
%这是建立一个空的结构体，field1，field2是域名称 
%s = struct('field1',values1,'field2',values2,...) 
%这是在建立结构体的时候就赋值，values1,values2就是针对field1,field2所赋的值。 
%例如：s = struct('type',{'big','little'},'color',{'red'},'x',{3 4}) 
%这个结构体有三个域'type','color','x'，根据英文意义可以看出分别是类型，颜色和值的意思。
%类型可以取的值有'big','little'，也就是类型有两种，分别是大和小。颜色只有'red'红色，而值x可以是3或者4
%
% 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;
    case 'ploy'
        d = ker.degree;
        c = ker.offset;
        K = (x'*y+c).^d;
    case 'gauss'
        
        s = ker.width;
        rows = size(x,2);
        cols = size(y,2);   
        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