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I'm getting an error (Index in position 1 exceeds array bounds)

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I'm trying to find the onset point of a transient signal by comparing it with a threshold value calculated based on the base-level of this signal. However, when I try to find the index of such a point it returns and index out of bounds, I can't figure out why. Here's my code
signal = maximum_env_ch2; % 65536x2 array (time, voltage)
max_thresh = max(signal(1:floor(0.3*end),2)); %threshold calculated form the first part of the signal (zero-level)
ind_out = find( signal > max_thresh ,1); %find index of point>thresh
onset = signal(ind_out,1); %return onset time

Accepted Answer

Jeffrey Clark
Jeffrey Clark on 5 Oct 2022
@Majd AG, find is going to look at the entire signal as if you had written signal(:) > max_thresh; find will return values beyond the first index limit. I expect you want:
ind_out = find( signal(:,2) > max_thresh ,1);
But also note that since max_thresh is from the signal it may be the actual max and therefore there is no signal(:,2)>max_thresh; find will return ind_out as an empty array which will also fail as an index.
  1 Comment
Majd AG
Majd AG on 8 Oct 2022
Thanks for the answer. indeed the problem was not specifiying the amplitude column (:,2) in find function.
and for your second note, in my case max_thresh is definitely not the maximum since it represent the highest point in the zero-level before the actual signal begins.

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More Answers (1)

Davide Masiello
Davide Masiello on 5 Oct 2022
Do this instead
ind_out = signal(1,:) > max_thresh; %find index of point>thresh
onset = signal(ind_out,1); %return onset time

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