How to get the highest value from the latest samples?

I have code that calculates an error for each sample, and I would like to always get the highest value from the last samples.

error(n,1)=Ia(n)-Ia_future(n,1)
p(n,1) = (1+0.2)*max(error(n-1,1))

I want to get the maximum value of the last n samples of error(n-1,1) that were calculated. The "max" above there is just to demonstrate what I'm trying to say.

[Rik]

You mean like max(error((end+1-n):end,1))?

Other than that, you should really not use error as a variable name.

[Luccas S.]

Yes, exactly that!

Answer 1

[Image Analyst]

error is a built-in function so don't call your variable that. Call it errors or differences instead.

Is this what you mean:

Ia_future = rand(5, 3) % Create sample data.
Ia = rand(5, 1)
% Initialize/preallocate p.
p = zeros(size(Ia));
[rows, columns] = size(Ia_future)
for n = 1 : rows % For every row...
    % We're now on iteration "n".  
    % Subtract the "last" n values, 
    % meaning the values we've seen "so far"
    % which would be the values from 1 to n.
    errorsSoFar = Ia(1:n) - Ia_future(1:n,1)
    % Put into an equation to get p.
    p(n) = (1+0.2)*max(errorsSoFar)
end

[Luccas S.]

I had already done the part with the for, I was having problems with the dimension, because the n-1 passed value didn't exist, it was like this:

 for n = 1:size(t,1)
     if  n>=4
         X = [Ia(n-1,1) Ia(n-2,1) ; Ia(n-2,1) Ia(n-3,1)];
         future = [Ia(n,1) ; Ia(n-1,1)];
         C = ((X.')*(X))'*(X.')*(future);
         Ia_future(n,1) = C(1,1)*Ia(n,1)+C(2,1)*Ia(n-1,1);
         PE(n,1)=Ia(n)-Ia_future(n,1);
         p(n,1) = (1+0.2)*max(PE((end+1-n):end,1)) % the part of Rik comment
     
        end
 end

[Image Analyst]

If you have an vector that you're indexing over in a loop, what do you consider the "last" values to be?

1. The values you've seen (indexed) already, so Ia(1:n), or (like "last" means last seen or "prior")
2. The rightmost values in the vector : Ia(end-n+1 : end) (the end of the array regardless of what the loop index is currently at)

[Luccas S.]

In the case I look for, the highest value among the samples already calculated. It doesn't have to be the largest value of the entire vector.

[Image Analyst]

So that would be case 1, and I gave code for that. But you didn't seem to try it. Why not?

[Luccas S.]

I just tested it, it worked.

I was thinking that I should disregard the n-1 value of the first sample but it wasn't necessary. Thanks!