function net = svmtrain(net, X, Y, alpha0, dodisplay)% 訓(xùn)練一個支持量機分類器% %   NET = SVMTRAIN(NET, X, Y)%   Train the SVM given by NET using the training data X with target values%   Y. X is a matrix of size (N,NET.nin) with N training examples (one per%   row). Y is a column vector containing the target values (classes) for%   each example in X. Each element of Y that is >=0 is treated as class%   +1, each element <0 is treated as class -1.%   SVMTRAIN normally uses L1-norm of all training set errors in the%   objective function. If NET.use2norm==1, L2-norm is used.%%   All training parameters are given in the structure NET. Relevant%   parameters are mainly NET.c, for fine-tuning also NET.qpsize,%   NET.alphatol and NET.kkttol. See function SVM for a description of%   these fields.%%   NET.c is a weight for misclassifying a particular example. NET.c may%   either be a scalar (where all errors have the same weights), or it may%   be a column vector (size [N 1]) where entry NET.c(i) corresponds to the%   error weight for example X(i,:). If NET.c is e vector of length 2,%   NET.c(1) specifies the error weight for all positive examples, NET.c(2)%   is the error weight for all negative examples. Specifying a different%   weight for each example may be used for imbalanced data sets.%%   NET = SVMTRAIN(NET, X, Y, ALHPA0) uses the column vector ALPHA0 as%   the initial values for the coefficients NET.alpha. ALPHA0 may result%   from a previous training with different parameters.%   NET = SVMTRAIN(NET, X, Y, ALPHA0, 1) displays information on the%   training progress (number of errors in the current iteration, etc)%   SVMTRAIN uses either the function LOQO (Matlab-Interface to Smola's%   LOQO code) or the routines QP/QUADPROG from the Matlab Optimization%   Toolbox to solve the quadratic programming problem.%%   See also:%   SVM, SVMKERNEL. SVMFWD%% % Copyright (c) Anton Schwaighofer (2001)% $Revision: 1.19 $ $Date: 2002/01/09 12:11:41 $% mailto:anton.schwaighofer@gmx.net% % This program is released unter the GNU General Public License.% % Training a SVM involves solving a quadratic programming problem that% scales quadratically with the number of examples. SVMTRAIN uses the% decomposed training algorithm proposed by Osuna, Freund and Girosi, where% the maximum size of a quadratic program is constant.% (ftp://ftp.ai.mit.edu/pub/cbcl/nnsp97-svm.ps)% For selecting the working set, the approximation proposed by Joachims% (http://www-ai.cs.uni-dortmund.de/DOKUMENTE/joachims_99a.ps.gz) is used.% 核對參數(shù)是否一致errstring = consist(net, 'svm', X, Y);if ~isempty(errstring);  error(errstring);end[N, d] = size(X);if N==0,  error('沒有給出訓(xùn)練樣本');endnet.nbexamples = N;if nargin<5,  dodisplay = 0;endif nargin<4,  alpha0 = [];elseif (~isempty(alpha0)) & (~all(size(alpha0)==[N 1])),  error(['ALPHA0的初始值必須是和X一樣長度的列向量']); end%從類+1和-1找到樣本的索引class1 = logical(uint8(Y>=0));class0 = logical(uint8(Y<0));if length(net.c(:))==1,  C = repmat(net.c, [N 1]);  %所有樣本一樣的上限elseif length(net.c(:))==2,  C = zeros([N 1]);  C(class1) = net.c(1);  C(class0) = net.c(2);  % 樣本類型+1和-1的不同的上限Celse  C = net.c;  if ~all(size(C)==[N 1]),    error(['上限C必須是和X一樣長度的列向量']);   endendif min(C)<net.alphatol,  error('NET.C必須為正并比NET.alphatol大');endif ~isfield(net, 'use2norm'),  net.use2norm = 0;endif ~isfield(net, 'qpsolver'),  net.qpsolver = '';endqpsolver = net.qpsolver;if isempty(qpsolver),  checkseq = {'quadprog', 'loqo', 'qp'};  i = 1;  while (i <= length(checkseq)),    e = exist(checkseq{i});    if (e==2) | (e==3),      qpsolver = checkseq{i};      break;    end    i = i+1;  end  if isempty(qpsolver),    error('No quadratic programming solver (QUADPROG,LOQO,QP) found.');  endend% Mind that there may occur problems with the QUADPROG solver. At least in% early versions of Matlab 5.3 there are severe numerical problems somewhere% deep in QUADPROG% Turn off all messages coming from quadprog, increase the maximum number% of iterations from 200 to 500 - good for low-dimensional problemsif strcmp(qpsolver, 'quadprog') & (dodisplay==0),  quadprogopt = optimset('Display', 'off', 'MaxIter', 500);else  quadprogopt = [];end% Actual size of quadratic program during training may not be larger than% the number of examplesQPsize = min(N, net.qpsize);chsize = net.chunksize;% SVMout contains the output of the SVM decision function for each% example. This is updated iteratively during training.SVMout = zeros(N, 1);%確保Y的值僅為+1和-1Y(class1) = 1;Y(class0) = -1;if dodisplay>0,  fprintf('Training set: %i examples (%i positive, %i negative)\n', ...	  length(Y), length(find(class1)), length(find(class0)));end% Start with a vector of zeros for the coefficients alpha, or the% parameter ALPHA0, if it is given. Those values will be used to perform% an initial working set selection, by assuming they are the true weights% for the training set at hand.if ~any(alpha0),  net.alpha = zeros([N 1]);  % If starting with a zero vector: randomize the first working set search  randomWS = 1;else  randomWS = 0;  % for 1norm SVM: make the initial values conform to the upper bounds  if ~net.use2norm,    net.alpha = min(C, alpha0);  endendalphaOld = net.alpha;if length(find(Y>0))==N,  % only positive examples  net.bias = 1;  net.svcoeff = [];  net.sv = [];  net.svind = [];  net.alpha = zeros([N 1]);  return;elseif length(find(Y<0))==N,  % only negative examples  net.bias = 1;  net.svcoeff = [];  net.sv = [];  net.svind = [];  net.alpha = zeros([N 1]);  return;enditeration = 0;workset = logical(uint8(zeros(N, 1)));sameWS = 0;net.bias = 0;while 1,  if dodisplay>0,    fprintf('\nIteration %i: ', iteration+1);  end  % 步驟1：決定支持向量  [net, SVthresh, SV, SVbound, SVnonbound] = findSV(net, C);  if dodisplay>0,    fprintf(['Working set of size %i: %i Support Vectors, %i of them at' ...	     ' bound C\n'], length(find(workset)), length(find(workset & SV)), ...	    length(find(workset & SVbound)));     fprintf(['Whole training set: %i Support Vectors, %i of them at upper' ...	     ' bound C.\n'], length(net.svind), length(find(SVbound)));    if dodisplay>1,      fprintf('The Support Vectors (threshold %g) are the examples\n', ...	      SVthresh);      fprintf(' %i', net.svind);      fprintf('\n');    end  end    % 步驟2: 找到SVM所有樣本的輸出  if (iteration==0) | (mod(iteration, net.recompute)==0),    % Every NET.recompute iterations the SVM output is built from    % scratch. Use all Support Vectors for determining the output.    changedSV = net.svind;    changedAlpha = net.alpha(changedSV);    SVMout = zeros(N, 1);    if strcmp(net.kernel, 'linear'),      net.normalw = zeros([1 d]);    end  else    % A normal iteration: Find the coefficients that changed and adjust    % the SVM output only by the difference of old and new alpha    changedSV = find(net.alpha~=alphaOld);    changedAlpha = net.alpha(changedSV)-alphaOld(changedSV);  end    if strcmp(net.kernel, 'linear'),    chunks = ceil(length(changedSV)/chsize);    % Linear kernel: Build the normal vector of the separating    % hyperplane by computing the weighted sum of all Support Vectors    for ch = 1:chunks,      ind = (1+(ch-1)*chsize):min(length(changedSV), ch*chsize);      temp = changedAlpha(ind).*Y(changedSV(ind));      net.normalw = net.normalw+temp'*X(changedSV(ind), :);                           %計算成本    end    % Find the output of the SVM by multiplying the examples with the    % normal vector    SVMout = zeros(N, 1);    chunks = ceil(N/chsize);    for ch = 1:chunks,      ind = (1+(ch-1)*chsize):min(N, ch*chsize);      SVMout(ind) = X(ind,:)*(net.normalw');    end  else    % A normal kernel function: Split both the examples and the Support    % Vectors into small chunks    chunks1 = ceil(N/chsize);    chunks2 = ceil(length(changedSV)/chsize);    for ch1 = 1:chunks1,      ind1 = (1+(ch1-1)*chsize):min(N, ch1*chsize);      for ch2 = 1:chunks2,	% Compute the kernel function for a chunk of Support Vectors and        % a chunk of examples	ind2 = (1+(ch2-1)*chsize):min(length(changedSV), ch2*chsize);	K12 = svmkernel(net, X(ind1, :), X(changedSV(ind2), :));	% Add the weighted kernel matrix to the SVM output. In update        % cycles, the kernel matrix is weighted by the difference of        % alphas, in other cycles it is weighted by the value alpha alone.	coeff = changedAlpha(ind2).*Y(changedSV(ind2));	SVMout(ind1) = SVMout(ind1)+K12*coeff;      end      if dodisplay>2,	K1all = svmkernel(net, X(ind1,:), X(net.svind,:));	coeff2 = net.alpha(net.svind).*Y(net.svind);	fprintf('Maximum error due to matrix partitioning: %g\n', ...		max((SVMout(ind1)-K1all*coeff2)'));      end    end  end    % Step 3: Compute the bias of the SVM decision function.  if net.use2norm,    % The bias can be found from the SVM output for Support Vectors. For    % those vectors, the output should be 1-alpha/C resp -1+alpha/C.    workSV = find(SV & workset);    if ~isempty(workSV),      net.bias = mean((1-net.alpha(workSV)./C(workSV)).*Y(workSV)- ...                      SVMout(workSV));    end  else    % normal 1norm SVM:    % The bias can be found from Support Vector whose value alpha is not at    % the upper bound. For those vectors, the SVM output should be +1    % resp. -1.    workSV = find(SVnonbound & workset);    if ~isempty(workSV),      net.bias = mean(Y(workSV)-SVMout(workSV));    end  end  % The nasty case that no SVs to determine the bias have been found.  % The only sensible thing do to is to leave the bias unchanged.  if isempty(workSV) & (dodisplay>0),    disp('No Support Vectors in the current working set.');