@(M)char(accumarray(((1:size(M,1))+(0:size(M,2)-1)')(:),M(:),[],@(x){num2str(x')})) ans([1 2 3; 4 5 6; 7 8 9])
Standard input is empty
ans = @(M) char (accumarray ((1:size (M, 1) + 0:size (M, 2) - 1') (:), M (:), [], @(x) {num2str(x')})) ans = 1 4 2 7 5 3 8 6 9