function s = sum(varargin)% GPVAR/SUM Implements sum function for GP variables.% % S = SUM(X) is the sum of the elements of the vector X.% If X is a matrix, S is a row vector with the sum over each column.%sz = size(varargin{1});if( length(varargin) == 1 )  % have a single input or an array input or a matrix input  if( max(sz) == 1 )     % single input, return it back    s = varargin{1};  elseif( sz(1) == 1 )    % have a row array    s = varargin{1}*ones(sz(2),1);  elseif( sz(2) == 1 )    % have a column array    s = ones(1,sz(1))*varargin{1};  else    % have a matrix (default is to sum over columns)    mtx = varargin{1};    for k = 1:sz(2)      col = mtx(:,k);       s(1,k) = ones(1,sz(1))*col;    end  endelse  % have an input list of scalar GP objects  s = posynomial;  for k = 1:length(varargin)    s = s + varargin{k};  endend