Another clearer and more general example, where a new leaf is added at each iteration: r = []; for i=1:4 nr = grand(2,2,"uin",0,9); r = matrix([ matrix(r,[1 size(r,"*")]) matrix(nr,[1 size(nr,"*")])],[2 2 i]) end By the way, you are right: A new concatenation operator along the third dimension could be useful. Samuel