You probably want something like
yt = [yt1, yt2, yt3, yt4, yt5] ;
and then use
yt(:,k)
in the loop, where k is the loop index. If yt's were not all the same dimension, you could use a cell array:
yt = {y1, y2, y3, y4, y5} ;
and then use
yt{k}
in the loop.
If you want to avoid copies/aggregation, just define directly the matrix the cell array instead of defining yt1 to yt5, e.g.
yt = zeros(200,5) ; % Prealloc.
yt(:,1) = ... whatever computation you used to define yt1
yt(:,2) = ... whatever computation you used to define yt2
..
or
yt{1} = ... whatever computation you used to define yt1
yt{2} = ... whatever computation you used to define yt2
