%SUBSC Subspace Classifier%%   W = SUBSC(A,N)%   W = SUBSC(A,FRAC)%% INPUT%   A          Dataset%   N or FRAC  Desired model dimensionality or fraction of retained %              variance per class%% OUTPUT%   W          Subspace classifier  %% DESCRIPTION% Each class in the trainingset A is described by linear subspace of% dimensionality N, or such that at least a fraction FRAC of its variance% is retained. This is realised by calling PCA(AI,N) or PCA(AI,FRAC) for% each subset AI of A (objects of class I). For each class a model is% built that assumes that the distances of the objects to the class% subspaces follow a one-dimensional distribution. %% New objects are assigned to the class of the nearest subspace.% Classification by D = B*W, in which W is a trained subspace classifier% and B is a testset, returns a dataset D with one-dimensional densities% for each of the classes in its columns.%% REFERENCE% E. Oja, The Subspace Methods of Pattern Recognition, Wiley, New York, 1984.%% See DATASETS, MAPPINGS, PCA, FISHERC, FISHERM, GAUSSM% Copyright: R.P.W. Duin, duin@ph.tn.tudelft.nl% Faculty of Applied Sciences, Delft University of Technology% P.O. Box 5046, 2600 GA Delft, The Netherlandsfunction W = subsc(A,N)  name = 'Subspace classf.';    % handle default  if nargin < 2, N = 1; end    % handle untrained calls like subsc([],3);  if nargin < 1 | isempty(A)    W = mapping(mfilename,{N});    W = setname(W,name);    return  end    if isa(N,'double')      % handle training like A*subsc, A*subsc([],3), subsc(A)  % PRTools takes care that they are all converted to subsc(A,N)          islabtype(A,'crisp');     % allow crisp labels only    isvaldset(A,1,2);         % at least one object per class, two objects    [m,k,c] = getsize(A);     % size of the training set    for j = 1:c               % run over all classes      B = seldat(A,j);        % get the objects of a single class only      u = mean(B);            % compute its mean      B = B - repmat(u,size(B,1),1); % subtract mean      v = pca(B,N);           % compute PCA for this class      v = v*v';               % trick: affine mappings in the original space      B = B - B*v;            % differences of objects and their mappings      s = mean(sum(B.*B,2));  % mean square error w.r.t. the subspace      data(j).u = u;          % store mean      data(j).w = v;          % store mapping      data(j).s = s;          % store mean square distance    end                              % define trained mapping,                              % store class labels and size    W = mapping(mfilename,'trained',data,getlablist(A),k,c);    W = setname(W,name);      elseif isa(N,'mapping')      % handle evaluation of a trained subspace classifier W for a dataset A.  % The command D = A*W is by PRTools translated into D = subsc(A,W)  % Such a call is detected here by the fact that N appears to be a mapping.        W = N;                    % avoid confusion: call the mapping W    m = size(A,1);            % number of test objects    [k,c] = size(W);          % mapping size: from K features to C classes    d = zeros(m,c);           % output: C class densities for M objects        for j=1:c                 % run over all classes      u = W.data(j).u;        % class mean in training set      v = W.data(j).w;        % mapping to subspace in original space      s = W.data(j).s;        % mean square distance      B = A - repmat(u,m,1);  % substract mean from test set      B = B - B*v;            % differences objects and their mappings      d(:,j) = sum(B.*B,2)/s; % convert to distance and normalise     end    d = exp(-d/2)/sqrt(2*pi); % convert to normal density        A = dataset(A);           % make sure A is a dataset     d = setdata(A,d,getlabels(W)); % take data from D and use                               % class labels as given in W                              % other information in A is preserved       W = d;                    % return result in output variable W      else             error('Illegal call')     % this should not happen      end  return