Max indices in for loop not changing after initial run (index exceeds the number or array elements)

I am getting the error

Warning: Error occurred while executing the listener callback for event ElementsAvailable defined for class daq.Buffer:
Index exceeds the number of array elements. Index must not exceed 3.

this error is occuring on my set function line in the code below. After pressing the "Start Button" on my UI(as seen below) and run it the first time after opening it it runs smoothly. after checking off additional channels it leads to errors. After the daq is done collecting and the user presses stop it writes the values to the workspace and I can see that it is still collecting those values even though they are not being displayed.

Any help is greatly appreciated!

function updateLivePlot(app)

   if isempty(app.DataFIFOBufferch1) || isempty(app.SelectedChannels)
       return
   end

   % Disable interactivity
   disableDefaultInteractivity(app.LiveAxes);

   % Keep the colors the same after each new data point
   app.LiveAxes.ColorOrderIndex = 1;

   if isempty(app.LivePlotLine)
       % First-Time Setup
           app.LivePlotLine = plot(app.LiveAxes, app.TimestampsFIFOBuffer, app.DataFIFOBufferch1(:,app.SelectedChannels));
   else
       % Update existing plot
       for j = 1:numel(app.SelectedChannels)  

           disp(j)

           % Check if the line needs to be extended
           if any(j <= numel(app.LivePlotLine)) && isempty(app.LivePlotLine(j))

               % Use existing axes to plot
               app.LivePlotLine(j) = plot(app.LiveAxes, app.TimestampsFIFOBuffer, app.DataFIFOBufferch1(:, j));
           else

               % Update existing line
               set(app.LivePlotLine(j), 'XData', app.TimestampsFIFOBuffer, 'YData', app.DataFIFOBufferch1(:, j));
           end
       end
   end
   if numel(app.TimestampsFIFOBuffer) > 1
       xlim(app.LiveAxes, [app.TimestampsFIFOBuffer(1), app.TimestampsFIFOBuffer(end)]);
   end
end

Answer 1

[Voss]

Looks like you already found an apparent solution, but I'll go ahead and point out the things I noticed, since they may still be useful for future debugging.

First, this condition is always false:

% Check if the line needs to be extended

if any(j <= numel(app.LivePlotLine)) && isempty(app.LivePlotLine(j))

The any is unnecessary because you are comparing two scalars, but also isempty(app.LivePlotLine(j)) is always false for the following reason:

app.LivePlotLine is a vector of line objects, so if j <= numel(app.LivePlotLine) then app.LivePlotLine(j) is a scalar, (i.e., a single line object). Since a scalar is not empty by definition, that condition is always false and the if branch there (i.e., the "Use existing axes to plot" line) is never executed.

So, ignoring that line and focusing on the "First-Time Setup" line and the "Update existing line" line, the relation between app.LivePlotLine and app.SelectedChannels seems inconsistent between the two.

When the first lines are created, you create as many lines as there are selected channels:

% First-Time Setup

app.LivePlotLine = plot(app.LiveAxes, app.TimestampsFIFOBuffer, app.DataFIFOBufferch1(:,app.SelectedChannels));

so that app.LivePlotLine(1) corresponds to app.SelectedChannels(1), app.LivePlotLine(2) corresponds to app.SelectedChannels(2), and so on. For example, if app.SelectedChannels is [2,5,9], then LivePlotLine(1) has data from channel 2, LivePlotLine(2) is channel 5, and LivePlotLine(3) is channel 9. No problem (yet).

However, later, when updating those same lines (suppose app.SelectedChannels is still [2,5,9]) in the "Update existing plot" branch, j runs from 1 to numel(app.SelectedChannels), so that this:

% Update existing line

set(app.LivePlotLine(j), 'XData', app.TimestampsFIFOBuffer, 'YData', app.DataFIFOBufferch1(:, j));

would be updating app.LivePlotLine(1) from channel 1 (not channel 2), app.LivePlotLine(2) from channel 2 (not channel 5), and app.LivePlotLine(3) from channel 3 (not channel 9).

Seems like it should be the following, which would be consistent with how the lines were created in the First-Time Setup:

% Update existing line

set(app.LivePlotLine(j), 'XData', app.TimestampsFIFOBuffer, 'YData', app.DataFIFOBufferch1(:,app.SelectedChannels(j)));

More generally, I think it's worth considering a simpler code design if possible, where you create as many lines as you have channels (all channels, not selected channels) when the app starts, giving you a nice 1:1 correspondence between channels and lines. Initially the lines can be invisible and have no data. When a channel is selected, the line becomes visible; when a channel is deselected, the line becomes invisible. When you update the lines' data, you only need to update the selected channels' lines, whose index in app.LivePlotLine is the same as app.SelectedChannels, because they are 1:1 now.

[Connor]

I used CHAT to help me but this is where it currently is at

function updateLivePlot(app)
   if isempty(app.DataFIFOBufferch1) || isempty(app.SelectedChannels)
       return
   end
   % Disable interactivity
   disableDefaultInteractivity(app.LiveAxes);
   % Keep the colors the same after each new data point
   app.LiveAxes.ColorOrderIndex = 1;
   % First-Time Setup
   if isempty(app.LivePlotLine)
       % Plot for the first time
       app.LivePlotLine = gobjects(size(app.SelectedChannels));  % Preallocate for efficiency
       for j = 1:numel(app.SelectedChannels)
           app.LivePlotLine(j) = plot(app.LiveAxes, app.TimestampsFIFOBuffer, app.DataFIFOBufferch1(:, app.SelectedChannels(j)));
           hold(app.LiveAxes, 'on');  % Hold for multiple plots
       end
   else
       % Update existing plot
       for j = 1:numel(app.SelectedChannels)
           % Check if the handle is still valid and within the bounds
           if j <= numel(app.LivePlotLine) && ishandle(app.LivePlotLine(j))
               set(app.LivePlotLine(j), 'XData', app.TimestampsFIFOBuffer, 'YData', app.DataFIFOBufferch1(:, app.SelectedChannels(j)));
           else
               % Re-plot if handle is invalid or out of bounds
               app.LivePlotLine(j) = plot(app.LiveAxes, app.TimestampsFIFOBuffer, app.DataFIFOBufferch1(:, app.SelectedChannels(j)));
               hold(app.LiveAxes, 'on');  % Hold for multiple plots
           end
       end
   end
   if numel(app.TimestampsFIFOBuffer) > 1
       xlim(app.LiveAxes, [app.TimestampsFIFOBuffer(1), app.TimestampsFIFOBuffer(end)]);
   end
end

I tried to do what you said above and I realized after wards that yes my code would still probably run into the same issues that you are describing. I end up getting errors when I try to use the set function with just

j = app.SelectedChannels

which I dont understand. I am concered about computer useage, how would you set up the channel visibility and have it plotting all channels?

[Voss]

j would stay as it was:

for j = 1:numel(app.SelectedChannels)

"how would you set up the channel visibility and have it plotting all channels?"

Create the lines all at once, e.g., in the startupFcn or wherever the total number of channels is determined, e.g.:

% N is the total number of channels
app.LivePlotLine = gobjects(1,N);
for ii = 1:N
    app.LivePlotLine(ii) = plot(app.LineAxes,NaN,NaN,'Visible','off');
end

Those lines are initially invisible because I'm presuming that all channels are initially not selected.

You could also use the line function instead of plot, but that requires setting the line colors yourself.

If the total number of channels can change while the app is running, you'd also have to add or delete lines to accomodate the new value.

When a channel is selected or deselected, set the corresponding element of app.LivePlotLine Visible property to 'on' or 'off' as appropriate.

Then your line update function is more simple:

function updateLivePlot(app)
    % update the lines for the SelectedChannels
    for j = 1:numel(app.SelectedChannels)
        set(app.LivePlotLine(app.SelectedChannels(j)), 'XData', app.TimestampsFIFOBuffer, 'YData', app.DataFIFOBufferch1(:, app.SelectedChannels(j)));
    end
    % set axes xlim
    if numel(app.TimestampsFIFOBuffer) > 1
        xlim(app.LiveAxes, app.TimestampsFIFOBuffer([1 end]));
    end
end

I'm assuming that the number of columns in app.DataFIFOBufferch1 is the total number of channels.

[Connor]

@Voss Thanks, I find when i use the plotting function the app runs quite slowly. How would you approach trying to just plot the app.selectedchannels using the set function. Would it be a good solution? I know you suggested using the channel visiblity but I am not sure if I can figure out how to optimize that for performance.

Thanks

[Voss]

My suggestion was to use plot to create the lines, and set to update them. Is the line creation the part that is slow?

[Connor]

yeah, Okay I do start with plot and then update with set so I will continue with that. While trying to go through and debugg the situation where if I select channels 1 and 3 rather ie channels with gaps inbetween them I noticed that it doesnt even show up as channels 1 and 3 selected, rather it shows up as 1,2 for both app.SelectedChannel & app.SelectedCal. I am using a find function to search throught he UItable and it doesnt seem to be working in the way I expected it to be.

This is the function that I use to find the T/F values of the UItable

function UITableCellEdit(app, event)
 
    
     % Update the Legends on the Axes based on the channel names      
     app.legnam = table2array(app.UITable.Data(:,1));
   
     % Update SelectedChannels based on ofchan
     app.SelectedChannels = find(table2array(app.UITable.Data(:,2)));
    
     % Update SelectedCal based on IndvCal
     app.SelectedCal = find(table2array(app.UITable.Data(:,3)));

    % Call the function that uses the selected channels (e.g., data calibration)
    updateChannelMeasurementComponents(app)

        end

the following is what I use for calibration.

        function calibratedData = calibrateData(app, data, slopes, intercepts)

    % Initialize calibrated data array

    calibratedData = data;

    % We want to make sure all channels selected are included to prevent
    % any errors from uccuring 
    for jj = app.SelectedChannels

            calibratedData(:,jj) = (data(:,jj));

    end

    
    for j = app.SelectedCal
            
            disp(j)
            
            % Apply calibration
            calibratedData(:, j) = (data(:, j) .* slopes(:,j)) + intercepts(:,j);         
    end

end

I am not use if their is a better way to do this but I hadnt even thought of the "if" someone is using it

thanks again for the help!

[Connor]

I was able to figure it out, the logic in the find function was fine I was just debugging impoperly. I think that I had to change back to

app.DataFIFOBufferch1(:, j) 
%from 
app.DataFIFOBufferch1(:,(app.SelectedChannels(i)))

becuase I was already going from 1:numel(app.SelectedChannels) in my for loop for the plotting and the calibrated data setup outside of the function had not been thoughly checked.

  if app.calibrate == true
    
       app.calibratedData = calibrateData(app,app.data, app.sl, app.int);
   else
       for jj = app.SelectedChannels

            app.calibratedData(:,jj) = (app.data(:,jj));

       end

   end

is now what I am using vs what was

     if app.calibrate == true
    
       app.calibratedData = calibrateData(app,app.data, app.sl, app.int);
     else

            app.calibratedData = app.data

   end

and inside the function my intial line

   app.calibratedData = app.data

that I was using for preallocation was creating 8 channels worth of column which would affect the calibration function and the plotting function later on in the code.

Answer 2

[Connor]

I fixed this by isomgpreaalocating of the app using

goobjects(size(app.SelectedChannels)) 

to give app.liveplotline the correct size