How can I resolve the subscripted assignment dimension mismatch error (for the cwt plot)?

Question

Navid 2023-11-22

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评论： Navid 2023-11-23

采纳的回答： Christopher McCausland

Hello,

I have an issue with the syntax used for the wavelet plot. The syntax used is:

[cfs(:,i), f(:,i)] = cwt(signal(:,i),fs(:,i)).

I have placed this syntax inside a for loop, where 'i' is the Excel sheet name. However, I am facing an error saying, "Subscripted assignment dimension mismatch." Can you please guide me on how to fix this error? I would appreciate any help you can provide.

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Answer 1

Christopher McCausland 2023-11-22

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在 MATLAB Online 中打开

Hi Navid,

Can you please post so information in relation to both your signal and fs variable? Or better yet attach them?

cfs, should probably be a three dimetional array, so:

cfs(:,:,i)

as the cwt will return a two dimentional image if this code is sitting in a for loop. However, until you give us a bit more information this is hard to solve, for example your input signal could be in columns, or may not be.

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Walter Roberson 2023-11-22

在 MATLAB Online 中打开

C1.xlsx

Sorry, I did not notice the R2016b; sheetnames() was added in R2019b.

filename = 'C1.xlsx';
% Get the sheet names
[~, sheetNames] = xlsfinfo(filename);
for i = 1:numel(sheetNames)
    % Read the data from the sheet
    data = xlsread(filename, i);
    
    % Extract the time and signal columns
    t(:,i) = data(:, 1);
    signal(:,i) = data(:, 2);
    dt = mean(diff(t(:,i))); % sampling time
    fs(i) = 1/dt; % freq
    [temp_cfs, temp_f] = cwt(signal(:,i), fs(i));
    whos temp_cfs temp_f
    cfs(:,:,i) = temp_cfs;
    f(:,i) = temp_f;
end
  Name            Size                  Bytes  Class     Attributes

  temp_cfs      104x10015            16664960  double    complex   
  temp_f        104x1                     832  double              

  Name            Size                  Bytes  Class     Attributes

  temp_cfs      104x10015            16664960  double    complex   
  temp_f        104x1                     832  double              

  Name            Size                  Bytes  Class     Attributes

  temp_cfs      104x10015            16664960  double    complex   
  temp_f        104x1                     832  double              

  Name            Size                  Bytes  Class     Attributes

  temp_cfs      104x10015            16664960  double    complex   
  temp_f        104x1                     832  double              

  Name            Size                  Bytes  Class     Attributes

  temp_cfs      104x10015            16664960  double    complex   
  temp_f        104x1                     832  double              

  Name            Size                  Bytes  Class     Attributes

  temp_cfs      104x10015            16664960  double    complex   
  temp_f        104x1                     832  double              

  Name            Size                  Bytes  Class     Attributes

  temp_cfs      104x10015            16664960  double    complex   
  temp_f        104x1                     832  double              

Christopher McCausland 2023-11-22

编辑：Christopher McCausland 2023-11-22

在 MATLAB Online 中打开

Hi Navid,

Can I ask why you want to do this?

While we can include plots in for loops, its generally considered bad practice. I am also not convinced about using contour as I do not think it convays the information well.

Regardless, please see attached contour as requested, and in addition via mesh() which I personally think convays the information better. The y-axis has been set to log to reflect the nature of the CWT. You should also note that this information is the same as a 2D cwt plot with a colour scale.

Christopher

filename = 'C1.xlsx';
% Get the sheet names
[~, sheetNames] = xlsfinfo(filename);
for i = 1:numel(sheetNames)
    % Read the data from the sheet
    data = xlsread(filename, i);
    
    % Extract the time and signal columns
    t(:,i) = data(:, 1);
    signal(:,i) = data(:, 2);
    dt = mean(diff(t(:,i))); % sampling time
    fs(i) = 1/dt; % freq
    [temp_cfs, temp_f] = cwt(signal(:,i), fs(i));
    whos temp_cfs temp_f
    cfs(:,:,i) = temp_cfs;
    f(:,i) = temp_f;
    
    
    % Begin plotting here, typically we would not do so in a for loop. 
    figure()
    contour(t(:,i),f(:,i),abs(cfs(:,:,i)).^2);
    set(gca, 'YScale', 'log');
    
    % Here is the same information presented with Mesh, which convays the data trends
    % better in my opinion.
    figure()
    mesh(t(:,i),f(:,i),abs(cfs(:,:,i)).^2)
    view(-30,60)
    set(gca, 'YScale', 'log');
end

Navid 2023-11-23

Dear Christopher,

I wanted to express my gratitude for the valuable guidance you provided me. This part of the code:

mesh(t(:,i),f(:,i),abs(cfs(:,:,i)).^2)

truthfully gives a deeper understanding of the signal.

However, sometimes, a 2D cwt plot may be more suitable for monitoring specific frequency ranges of a signal.

Thank you for taking the time to share your knowledge with me. Your guidance has been instrumental in helping me improve my work, and I greatly appreciate it.

Best regards,

Navid

Navid 2023-11-23