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problem in applying loop

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Ali Asghar
Ali Asghar 2019-9-18
评论： Ali Asghar 2019-9-19
I have emg signal (30000x4) and want to apply function on it in loop....
function waveLen = find_waveform_length(signal)
sum=0;
for i=2:length(signal)
sum= sum + abs(signal(i)-signal(i-1));
end
waveLen = sum;
%%%%%% New file %%%%%%%
load ('dath001.mat');
x = dath001; % 30000x4
for i = 1:4
waveLen(i) = find_waveform_length(x(i))
end
but it give output of 0 0 0 0
instead if i run waveLen function separately it give output of
463.6428 200.0671 411.7511 372.9306 ... I want this output by simple apply loop command
Thank you

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Raj
Raj 2019-9-18
What is the 'y' you have used in your main script loop? Its not defined anywhere. Use this line in main script:
waveLen(i) = find_waveform_length(x(:,i))
Since you have not shared your MAT file, I tried with a random 30000x4 matrix and it works.
Few other recommendations:
1) Put an 'end' for your function
2) Don't use variable 'i' or any other inbuilt Matlab variable as index in your 'for' loop.
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Raj
Raj 2019-9-18
Again you have not mentioned what is 'y' here.
Lets see your expression in the loop:
datawindow(i) = w.*buffer(y(:,i),2000,-500)
You are trying to dynamically name the variable datawindow. It is not recommended. See this:
https://www.mathworks.com/matlabcentral/answers/304528-tutorial-why-variables-should-not-be-named-dynamically-eval
Now coming to your error. The right side of this expression will give you a matrix of some size and you are trying to assign that to a single element of matrix datawindow hence you are getting the size mismatch error.
Wayout: Define datawindow as a cell array like this:
datawindow=cell(4,1);
Then in your loop use this expression:
datawindow(i,1) = {w.*buffer(y(:,i),2000,-500)};
Now your datawindow will have 4 matrices as cell elements. You can extract and use them like this:
datawindow1=cell2mat(datawindow(1,1));
and so on.
See these links for details:
https://www.mathworks.com/help/matlab/ref/cell.html
https://www.mathworks.com/help/matlab/ref/cell2mat.html

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