function main()

    combv({[1,2,3], [3,4,5]})

    function currset = combv( superset )
    % COMBV returns all combinations of a given set of vectors. 'superset' is
    % a cell array of vectors to be combined. The output is an array of
    % combined vectors. combv is a recursive function. [adam greenberg]
    % Note that the output array returned by combv lists combinations of vector
    % elements in row-major order, whereas the MATLAB built-in combvec function
    % returns combinations in column-major order. To make combv output match
    % combvec, call combv as combv( superset )' .
    
        % combv works by recursing down the cell array of vectors. once it gets
        % to the bottom, it starts building up the output array by combining
        % the last vector of the input array with the penultimate vector. at
        % its core, combv is performing a simple map-reduce.
        
        numlevel = length( superset );
        numcurr = length( superset{1} );
        
        % if there are any vectors left in this copy of the superset, call
        % combv on those vectors.
        subset = [];
        if numlevel>1
            subset = combv( superset(2:end) ); % recurse
        end
        numsub = size(subset,1);
        dimsub = max(1,numsub);
        
        % combine the current level's vector elements with all the vector
        % combinations that were determined by previous recursive calls of
        % combv. if there was no previous recursive calls (i.e., this level is
        % the lowest) then the internal for loop is skipped.
        currset = zeros( [ dimsub*numcurr numlevel ] );
        for i=1:numcurr
            icurr = (i-1)*dimsub + 1;
            currset( icurr:icurr+dimsub-1, 1 ) = superset{1}(i);
            for j=1:numsub
               isub = j-1;
               currset( icurr +  isub, 2:end ) = subset(j,:);
            end
        end
    end

end