matlab


finding the max index in a moving window


I want to find the max element's index for a moving window. I tried to do it as the following (a simple example):
x=[1,2,3,4,5,6,7,8,9];
[m,I]=max(x(1:5))
ans
m=5
I=5
then if I say
[m2,I2]=max(x(3:7));
I get
ans
m2=7
I2=5
I want a way to give me the index with reference to the original big vector not the subvector which was passed to the function (I want I2 to give me 7 not 5).
Is there a way to do so?
Thanks
You can do something like this:
x = [2,5,6,8,4,5,10,33];
start_w = 4;
end_w = 7;
[m,I] = max(x(start_w:end_w));
I = I + start_w - 1; %reindex to x, so that x(I)==m
you can use sliding window operation to get the local max indexes and add the global window xenter indexes afterwards:
function idx = maxidx(x)
[~,idx] = max(x);
and:
x = [1,2,3,4,5,6,7,8,9,1,3]; % test array
W = 5; % window width
% moving max idx function -> local indexes
B = colfilt(x,[1 W],'sliding',#maxidx);
% index addition to convert local indexes to global
addedIdx = (1:length(x)) - floor((W+1)/2);
% add local indexes with global addition
res = B + addedIdx
res =
3 4 5 6 7 8 9 9 9 9 9

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