It can probably be done without a loop, but why do you want that? Loops are very efficient (as long as there isn't a builtin vectorized alternative).
T={1,2,3};
ind_list=nchoosek(1:numel(T),2)
This is not the order you want, so we will need to use something else:
ind_list=(1:numel(T)).'+(0:1);
ind_list=mod(ind_list,numel(T));
ind_list(ind_list==0)=numel(T);
ind_list
Now we can loop through the rows of ind_list to create S:
S=cell(size(ind_list,1),1);
for n=1:size(ind_list,1)
tmp=T(ind_list(n,:));
tmp=horzcat(tmp{:});
S{n}=tmp;
end
S
