MATLAB: How to calculate the maximum of different parts of a vector without using a for loop

Question

Hi!

I have a vector H, which is separated in different events of known size, i.e. s=[2,5,7,2,…] and I want to find the maximum that corresponds to each event. How can I do it without using a for loop (I want to reduce the computational time)?

Using a for loop would be:

maxH(1) = max(H(1:s(1)));
for i=2:length(s)
  maxH(i) = max(H( 1+sum(s(1:i-1)) : sum(s(1:i-1)) + s(i) ));
end

Thanks!

[EDITED, Jan, code formatted]

Answer 1

Although I don't recommend programming like this in MATLAB, sometimes writing out the logic out explicitly can make it run extremely fast. MATLAB has become very good at loops you know:

maxH = zeros(numel(s),1);
V = 1;
thismax = -inf;
thiss = s(1);
cnt = 1;
N = numel(H);
for n = 1:N
    if cnt > thiss
        maxH(V) = thismax;
        thismax = H(n);
        V = V+1;
        cnt = 1;
        thiss = s(V);
    elseif H(n) > thismax
        thismax = H(n);
    end
    cnt = cnt+1;
end
maxH(V) = thismax;