problem in applying loop

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

Answer 1

[Raj]

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.

[Ali Asghar]

Thank you dear

[Ali Asghar]

Dear

now i want to apply windowing in it....

previously i did in below way

w = hann(2000);

datawindow1 = w.*buffer(y(:,1),2000,-500); % buffer is good command, read it

datawindow2 = w.*buffer(y(:,2),2000,-500);

datawindow3 = w.*buffer(y(:,3),2000,-500);

datawindow4 = w.*buffer(y(:,4),2000,-500);

but when i do it in loop like

for i = 1:4

datawindow(i) = w.*buffer(y(:,i),2000,-500)

end

it shows error

Unable to perform assignment because the indices on the left side are not compatible with the size of the right side.

[Raj]

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

[Ali Asghar]

oky dear