Can anyone tell me why this error is occurring and how to solve it? Thank you.

I am getting modwt (line138) error saying invalid transform level. I have tried using different ecg data files in mat format from physionet atm.

Code:

%program to get QRS peaks and Heart Rate from ECG signal
[filename,pathname]=uigetfile('*.*','Select the ECG Signal');
filewithpath=strcat(pathname,filename);
Fs=input('Enter Sampling Rate:  ');

ecg=load(filename);   %Reading ECG signal
wecg=(ecg.val)./200; %Normalize gain
t=1:length(wecg);   %No. of samples
tx=t./Fs;              %Getting Time vector

wtecg= modwt(wecg,4,'sym4');  %4-level undecimated DWT using sym4  //this is where the error is occurring//
wtrec=zeros(size(wtecg));
wtrec(3:4,:)= wtecg(3:4,:);   %Extracting only d3 and d4 coefficients.

Answer 1

[William Rose]

@Rafia Noshin, please include a sample ecg data file so we can run the code.

What error do you get? When I run that line, I get no error:

wecg=rand(1,2000);
wtecg= modwt(wecg,4,'sym4');
disp(size(wtecg))

           5        2000

It runs without error for me.

[William Rose]

[edit: changed my description of the relation between level and number of points]

If the signal duration is less that 2^level, you will get the invalid level error:

level=4; N=16;
wecg=rand(1,N);
wtecg= modwt(wecg,level,'sym4');  % N>=2^level: no error
disp(size(wtecg))

     5    16

But if you have 15 or fewer points, you get the invalid level error:

level=4; N=15;
wecg=rand(1,N);
wtecg= modwt(wecg,level,'sym4');  % N<2^level: error!

Error using modwt
Invalid transform level.

I doubt your signal is that short.

[Rafia Noshin]

How to determine the number of points of the ecg signal being used? Could you kindly share the file you have used that gave you no error?

This is the time length of the signals I have used. Also, I have attached the ecg data files I have tried using for this code.

[William Rose]

@Rafia Noshin,

In the code below, I load one of your files and compute the wavelet transform.

ecg=load('r01_edfm');   %the data in the file is a structure
ecgVal=ecg.val;         %extract the numeric data from the structure
level=4;
wtecg= modwt(ecgVal(1,:),level,'sym4'); 
disp(size(wtecg))

           5       10000

The code above works without error.

[Rafia Noshin]

I am trying to obtain the graph for the signal too. This is the graph I am getting after running the modified code you have given.

[William Rose]

@Rafia Noshin,

Your original question was how to solve an error when calling modwt(). We have solved that error and therefore answered that question. If you have a new question, please post it as a new question on Matlab Answers (after searching to see if it has already been answered, of course). When you do, please include the data and code. Please simplify the code as much as possible so that the error is clear and so that others can assist you.

When you include code, please highlight it and format it as code, and run it in the Matlab Answers window. This will allow others to see the output of your script, including errors or warnings.

[Rafia Noshin]

Okay. Thank you for answering my question.

[William Rose]

@Rafia Noshin, youre welcome. Good lcuk with your work.