all loop values in one vector

what is the problem please ?

z=[];
for n=2:length(acc_norm)-1;
    if abs(acc_norm(n,:))>max(abs(acc_norm(n-1,:)),abs(acc_norm(n+1,:)))
        Sc='Speak';
    elseif abs(acc_norm(n,:))<min(abs(acc_norm(n-1,:)),abs(acc_norm(n+1,:)))
        Sc='Svalley';
    else Sc='Sintmd';
    end
    z=[z;Sc];
end

Answer 1

[Walter Roberson]

Remember that strings are not entities in themselves: strings are row vectors of characters. So Sc='Speak'; is setting Sc to a row vector of length 5, and Sc='Svalley' is a row vector of length 7. Your z=[z;Sc] is then attempting to put together row vectors of different lengths.

I suggest you use

z{end+1} = Sc;