samer@4: % foldcols :; 
samer@4: %    ([[M]], [[N]] -> [[M]])   ~'folding function',
samer@4: %    [[M]]                     ~'initial value',
samer@4: %    [[N,L]]                   ~'data to scan, sequence of length L'
samer@4: % -> [[M]].
samer@4: 
samer@4: function y=foldrcols(f,y,X,varargin)
samer@4: 	if nargin>3
samer@4: 		opts=prefs('draw',0,varargin{:});
samer@4: 		for i=size(X,2):-1:1
samer@4: 			y1=f(y,X(:,i));
samer@4: 			if opts.draw
samer@4: 				opts.plotfn(i,y,X(:,i),y1); 
samer@4: 			end
samer@4: 			optpause(opts);
samer@4: 			y=y1;
samer@4: 		end
samer@4: 	else % streamlined version
samer@4: 		for i=size(X,2):-1:1, y=f(y,X(:,i)); end
samer@4: 	end
samer@4: 	
samer@4: