ssvr_srstrain.m

本人编的一个程序

function [alpha,sv,beta,time,obj] = ssvr_srstrain(samples,labels,param)
%
% [alpha,sv,beta] = ssvr_srstrain(samples,targets,param)
% This function builds sparse insensitive Huber kernel regression by a mathcing pursuit method.
% The subroutine requires the following input:
%       samples:  n x d sample matrix
%       targets:  n x 1 target vector
%       param:    param.kernel,param.kernelparam,param.lamda,param.epsilon, param.delta

% The routine returns
%       alpha:    vector of expansion coefficients
%       sv:       indices of support vectors
%       beta:     matrix of expansion coefficients
%

if (nargin ~= 3) % check correct number of arguments
    help ssvr_srstrain
else
    fprintf('Sparse Support Vector Regression by Selecting a Reduced Set ............\n')
    tic;

    % set the initial parameters
    n = length(labels);
    time = zeros(param.nsv,1);
    K = []; R = [];
    sv = []; nonsv = 1:n;
    alpha = []; beta = zeros(param.nsv,param.nsv);
    obj = [];
    r = -labels;
    I0 = find(abs(r) <= param.epsilon);
    I1 = find(abs(r) > param.epsilon & abs(r) <= param.delta);
    I2 = find(abs(r) > param.delta);
    if param.trace
        fprintf('Step\t\t\tObj\t\t\t\t\t\tAdded\n');
    end
    
    % loops until a specified number of basis functions is reached
    for i = 1:param.nsv

        % select the basis function to be included from a random subset of
        % candidates (exclude those which has already been selected)
        num = min(100,length(nonsv));
        perm = randperm(length(nonsv));
        tsamples = samples(nonsv(perm(1:num)),:);
        TK = evalkernel(samples,tsamples,param.kernel,param.kernelparam);
        normcoff = sum(TK.^2)';
        term = zeros(n,1); 
        term(I1) = 2*(abs(r(I1)) - param.epsilon).*sign(r(I1)); 
        term(I2) = 2*(param.delta - param.epsilon)*sign(r(I2));
        term(sv) = term(sv) + 2*param.lamda*alpha;
        score = -(TK'*term).^2./normcoff/sum(term.^2);
        [temp,tindex] = min(score);
        index = nonsv(perm(tindex));
        nonsv(perm(tindex)) = [];
        addK = TK(:,tindex);
        
        % solve the subprolbem including the new basis function
        K = [K addK];
        x = K(I1,i); 
        X = K(I1,1:i-1);
        diag_k = x'*x + param.lamda*TK(index,tindex); % diagonal element k in K'K + param.lamda*K matrix
        col_k = x'*X + param.lamda*TK(sv,tindex)'; % elements of column k in K'K + param.lamda*K matrix
        R = cholinsert(R,diag_k,col_k); % Cholesky insert of the Hessian            
        sv = [sv; index];
        alpha = [alpha; 0];
        [alpha,R,r] = finiteNewton(R,r,K,labels,param,alpha,I0,I1,I2,sv);
        
        % update I0, I1 and I2, and output the current objective value
        beta(1:i,i) = alpha;
        I0 = find(abs(r) <= param.epsilon);
        I1 = find(abs(r) > param.epsilon & abs(r) <= param.delta);
        I2 = find(abs(r) > param.delta);
        obj = [obj; sum((abs(r(I1)) - param.epsilon).^2)...
            + (param.delta - param.epsilon)*sum(2*abs(r(I2)) - param.delta - param.epsilon)...
            + param.lamda*alpha'*(r(sv) + labels(sv))];
        if param.trace
            fprintf('%d\t\t\t\t%d\t\t\t%d\n', i, obj(i),index);
        end
        time(i,1) = toc;
    end
    
    fprintf('Execution time : %4.1f seconds\n',time(end));    
    
end

function [alpha,R,r] = finiteNewton(R,r,K,labels,param,oldalpha,oldI0,oldI1,oldI2,sv)

while 1
    
    % compute the Newton direction
    c = K([oldI1;oldI2],:)'*[labels(oldI1) + param.epsilon*sign(r(oldI1));...
        - (param.delta - param.epsilon)*sign(r(oldI2))];
    h = R\(R'\c) - oldalpha;
    
    % exaxt line search
    u = K*h;
    grad = 2*K(oldI1,:)'*(r(oldI1) + labels(oldI1)) + 2*param.lamda*(r(sv) + labels(sv)) - 2*c;
    coff(1,1) = h'*grad;
    coff(1,2) = 2*u(oldI1)'*u(oldI1) + 2*param.lamda*h'*u(sv);
    t = svrexactlinesearch(coff,r,u,param.epsilon,param.delta,oldI0,oldI1,oldI2); 
    
    % compute the new alpha and r
    alpha = oldalpha + t*h;
    r = r + t*u;
    I0 = find(abs(r) <= param.epsilon);
    I1 = find(abs(r) > param.epsilon & abs(r) <= param.delta);
    I2 = find(abs(r) > param.delta);
    
    % Cholesky update
    index = setdiff(I1,oldI1);
    for i = 1:length(index)
        R = cholupdate(R,K(index(i),:)','+');
    end
    index = setdiff(oldI1,I1);
    for i = 1:length(index)
        R = cholupdate(R,K(index(i),:)','-');
    end
   
    % return if the stop condition is reached 
    if isempty(setxor(I1,oldI1)) & isempty(setxor(I2,oldI2))
        break;
    end
    
    % update oldI0, oldI1, oldI2 and oldalpha
    oldI0 = I0;
    oldI1 = I1;
    oldI2 = I2;
    oldalpha = alpha;
end

function R = cholinsert(R, diag_k, col_k)
% Cholesky insert

if isempty(R)
  R = sqrt(diag_k);
else
  R_k = R'\col_k'; % R'R_k = (K'K)_k + param.lamda*K, solve for R_k
  R_kk = sqrt(diag_k - R_k'*R_k); % norm(x'x) = norm(R'*R), find last element by exclusion
  R = [R R_k; [zeros(1,size(R,2)) R_kk]]; % update R
end

function t = svrexactlinesearch(coff,r,u,epsilon,delta,nonsv,sv1,sv2)
%
% This function performs the exact line search for insensitive Huber loss function.
% The subroutine requires the following input:
%       coff:  initial coefficients
%       r:     residual vector
%       u:     K*h
%       epsilon: parameter of loss function
%       delta: parameter of loss function
%       nonsv: the index of non-support vectors
%       sv1:   the index of the support vectors lying in the quadratic loss
%       sv2:   the index of the support vectors lying in the linear loss
% The routine returns
%       t:     step size
%

if norm(u) < eps
    t = 0;
    return;
end
% from zero loss to the quadratic loss, the linear loss
index = find(abs(u(nonsv)) > 0);
index = nonsv(index);
kv = [(sign(u(index))*epsilon - r(index))./u(index) index]; % enter the quadratic loss
kv = [kv; [(sign(u(index))*delta - r(index))./u(index) -index]]; % leave the quadratic loss

% from quadratic loss to the other loss
index1 = find(r(sv1).* u(sv1) > 0);
index1 = sv1(index1);
kv = [kv; [(sign(u(index1))*delta - r(index1))./u(index1) -index1]]; % enter the linear loss
index2 = find(r(sv1).* u(sv1) < 0);
index2 = sv1(index2);
kv = [kv; [(-sign(u(index2))*epsilon - r(index2))./u(index2) -index2]]; % enter the zero loss
kv = [kv; [(sign(u(index2))*epsilon - r(index2))./u(index2) index2]]; % enter the quadratic loss
kv = [kv; [(sign(u(index2))*delta - r(index2))./u(index2) -index2]]; % enter the linear loss

% from linear loss to the other loss
index = find(r(sv2).* u(sv2) < 0);
index = sv2(index);
kv = [kv; [(-sign(u(index))*delta - r(index))./u(index) index]]; % enters the quadratic loss
kv = [kv; [(-sign(u(index))*epsilon - r(index))./u(index) -index]]; % enters the zero loss
kv = [kv; [(sign(u(index))*epsilon - r(index))./u(index) index]]; % again enters the quadratic loss
kv = [kv; [(sign(u(index))*delta - r(index))./u(index) -index]]; % enters the linear loss

% sort the kink values
[temp ind] = sort(kv(:,1));
kv = kv(ind,:);

% compute the step length
kv = [kv; [Inf,0]];
leng = size(kv,1);
for i = 1:leng
    if  coff(1,1) + kv(i,1)*coff(1,2) > 0
        t = -coff(1,1)/coff(1,2); 
        break;
    else  % update coefficients
        if kv(i,2) > 0
            ind = abs(kv(i,2));
            coff(1,1) = coff(1,1) - 2*kv(i,1)*u(ind)^2;
            coff(1,2) = coff(1,2) + 2*u(ind)^2;
        else
            ind = abs(kv(i,2));
            coff(1,1) = coff(1,1) + 2*kv(i,1)*u(ind)^2;;
            coff(1,2) = coff(1,2) - 2*u(ind)^2;
        end
    end
end