wolffd@0: function [deltas, idx, weights] = get_fo_deltas(r, X, rectify)
wolffd@0: % [deltas, idx, (weights)] = get_fo_deltas(r, X)
wolffd@0: % 
wolffd@0: % returns the difference vectors (dist(a,c) > dist(a,b)) 
wolffd@0: %  for a given ranking: 
wolffd@0: %  deltas{i}(:,1) = a - b, deltas{i}(:,2) = a - c; 
wolffd@0: %
wolffd@0: % set rectify to output absolute values of training examples
wolffd@0: 
wolffd@0: if nargin < 3
wolffd@0:     rectify = 0;
wolffd@0: end
wolffd@0: 
wolffd@0: % ---
wolffd@0: % NOTE: this preallocation is not complete
wolffd@0: % ---
wolffd@0: deltas = {};
wolffd@0: idx = {};
wolffd@0: weights = [];
wolffd@0: for i = 1:size(r,1)
wolffd@0:     
wolffd@0:     % feature index
wolffd@0:     a = i;
wolffd@0:     
wolffd@0:     % check if ranking is valid
wolffd@0:     if ~isempty(r{i,1}) && ~isempty(r{i,2})&& ...
wolffd@0:         isempty(intersect(r{i,1}, r{i,2}));
wolffd@0:     
wolffd@0:         % ---
wolffd@0:         % NOTE / TODO: the follwing is intended for compability
wolffd@0:         %  both sides of the ranking may have more than one entry.
wolffd@0:         %  for the MTT database, the ranking may be correct, but the 
wolffd@0:         %  inequalities build from non-singular rankings are not
wolffd@0:         %  based on the actual data
wolffd@0:         % ---
wolffd@0:         for j = 1:numel(r{i,1})
wolffd@0:             b = r{i,1}(j);
wolffd@0:             
wolffd@0:             for k = 1:numel(r{i,2})
wolffd@0:                 c = r{i,2}(k);
wolffd@0: 
wolffd@0:                 % ---
wolffd@0:                 % get vector deltas, 
wolffd@0:                 % NOTE: first: dissimilar, then similar pair
wolffd@0:                 % ---
wolffd@0:                 [dac] = X(:,a) - X(:,c);
wolffd@0:                 [dab] = X(:,a) - X(:,b);
wolffd@0: 
wolffd@0:                 if ~rectify
wolffd@0:                     deltas{end+1} = [dac dab]; 
wolffd@0:                 else
wolffd@0:                     % ---
wolffd@0:                     % rectify the data for training
wolffd@0:                     % ---
wolffd@0:                     deltas{end+1} = abs([dac dab]); 
wolffd@0:                 end
wolffd@0:                 
wolffd@0:                 idx{end+1} = {[a c],[a b]};
wolffd@0:                 
wolffd@0:                 % save weights
wolffd@0:                 if size(r,2) == 3
wolffd@0:                     weights(end+1) = r{i,3}(1);
wolffd@0:                 end
wolffd@0:             end
wolffd@0:         end
wolffd@0:     end
wolffd@0: end
wolffd@0: end
wolffd@0: