Google's Winner Takes All hashing implemmentation

WTA_kernel_binary

function[binary_codes,G_vecs] = WTA_kernel_binary(X,G_vecs,G, K)
% G is number of permutation vectors
% K is the insterest span

if size(G_vecs,1) == 0
        G_vec = zeros(G,size(X,2));
        for i = 1:G 
                G_vecs(i,:) = randperm(size(X,2),size(X,2));
        end
end

c = zeros(size(X,1),G*K);

binary_codes = zeros(size(X,1),K*G);

for i = 1:G 
        interest_segment = X(:,G_vecs(i,1:K));
        codes = zeros(size(X,1),K);
        
     
        [max_vals, max_indx] = max(interest_segment, [], 2);
        [min_vals, min_indx] = min(interest_segment, [], 2);
        
        max_indx = bsxfun(@eq,interest_segment,max_vals);
        min_indx = bsxfun(@eq,interest_segment,min_vals);
        
        codes(max_indx) = 1;
        codes(min_indx) = -1;
        
        star_column = ((i-1)*K+1);
        end_column = (i*K);
        binary_codes(:,star_column:end_column) = codes;
end

% slower but better discimrimination

% for i = 1:G 
%         interest_segment = X(:,G_vecs(i,1:K));
%         codes = zeros(size(X,1),K);
%         
%         for j = 1:size(X,1)
%              unique_items = unique(interest_segment(j,:));
%              
%              % Check all same
%              if numel(unique_items) == 1
%                  codes(j,:) = zeros(1,size(interest_segment,2));
%              else
%                  [max_val, min_ind] = max(interest_segment(j,:));
%                  max_val_indices = find(interest_segment(j,:) >= max_val);
%                  codes(j,max_val_indices) = 1;
%                  
%                  [min_val, min_ind] = min(interest_segment(j,:));
%                  min_val_indices = find(interest_segment(j,:) <= min_val);
%                  codes(j,min_val_indices) = -1;
%              end
%         end
%         star_column = ((i-1)*K+1);
%         end_column = (i*K);
%         binary_codes(:,star_column:end_column) = codes;
% end