Waitbar does not increment

I am trying to use waitbar to show the progress of a for loop that is stepping through a data file using memmapfile and doing array arithmetic on the data. The bar remains at 0 until the loop exits and then jumps to full scale in one jump. I have tried adding a refresh or a drawnow following the waitbar update with no success. I have run the approxpi example from help and that runs correctly. The loop, which works correctly, looks like this: (somewhat simplified, leaving out the array definitions and the full table structure)

    Previous_Frequency =  0;
    Current_Frequency = 0;

    Data_Offset = PCT_Count + (4 * Echo_Count); % total size of pulse table and data block in bytes
  hwb = waitbar(0, 'Getting the data, Please wait');
  j = ones(1, 1,'int32'); % new frequency counter
  for p = 1 : Total_pulse_Count
    waitbar(p / Total_pulse_Count, hwb);
    Byte_Offset = PCT_Offset + ( (p - 1) * Data_Offset);

    PCT = memmapfile (Full_Name, 'Offset', Byte_Offset, 'Repeat', 1, 'Format', {    
        'int32'  [1 1]    'record_id'          ; 
      %etc etc       
    });   % Format and object end. Length 144 bytes

    PCT_Data = memmapfile (Full_Name, 'Offset', Byte_Offset +       PCT_Count, 'Repeat', 1, 'Format', { 
        'int16' [2 eval(num2str(Num_Receivers)) eval(num2str(Num_Gates))] 'IQRxRG'         
        });   % Format and object end.

        TempIQ = PCT_Data.Data(1).IQRxRG; % read the data into memory for faster access
        TempIQ = swapbytes(TempIQ);

        Current_Frequency = PCT.data.frequency;
        if p == 1 % special case, first loop
            Previous_Frequency = Current_Frequency;
            Frequency_Scale(j, 1) = PCT.data.frequency;
        end
        if Current_Frequency ~= Previous_Frequency % increment the new frequency counter, update Frequency Scale
            j = j + 1; 
            if j > Frequency_Count, break, end
            Frequency_Scale(j, 1) = PCT.data.frequency;
        end;
        for m = 1 : Num_Receivers;
            for k = 1 : Num_Gates % integrate each signal and calculate the magnitude for each antenna
                if Current_Frequency ~= Previous_Frequency % start a new integration
                    Plot_Data_Ant(k, j - 1, m) = (I(k, m)^2 + Q(k, m)^2)^0.5; % Write the earlier loop data
                    I(k, m) = (TempIQ(1,m,k));
                    Q(k, m) = (TempIQ(2,m,k));
                    IT(k, j) = IT(k, j) + I(k, m);
                    QT(k, j) = QT(k, j) + Q(k, m);
                else
                    I(k, m) = I(k, m) + (TempIQ(1,m,k));
                    Q(k, m) = Q(k, m) + (TempIQ(2,m,k));
                    IT(k, j) = IT(k, j) + (TempIQ(1,m,k));
                    QT(k, j) = QT(k, j) + (TempIQ(2,m,k));
                end
             end
        end
        for k = 1 : Num_Gates % calculate the magnitude for all the antennas
           Plot_Data_All(k, j) = (IT(k, j)^2 + QT(k, j)^2)^0.5;
        end
        Previous_Frequency = Current_Frequency;
    end;
    Plot_Data_Ant(k, j, m) = (I(k, m)^2 + Q(k, m)^2)^0.5;
    close(hwb);

[Walter Roberson]

Why are you using

[2 eval(num2str(Num_Receivers)) eval(num2str(Num_Gates))]

instead of the much more straight-forward

[2 Num_Receivers Num_Gates]

??

Answer 1

[Fangjun Jiang]

Inside the for-loop, can you try adding either "drawnow" or "pause(0.2)" after the waitbar() statement?

I never had problem regarding updating the waitbar figure. Maybe you can comment out some of the code inside the loop to see what happens.

[Walter Roberson]

My memory is that waitbar() includes a drawnow() in its code. Unfortunately I cannot check that at the moment.

[Fangjun Jiang]

It does. So I guess adding drawnow is not needed. I am not sure if pause() will help. Just throw some ideas.

[Walter Roberson]

Ah... I just remembered -- doesn't waitbar() have a rate limiter built in, so that it only updates every second or two? Stores the elapsed time as a property of the waitbar patch, and only updates the patch if enough time has passed ?

If my memory is correct, then waitbar() would not increment for any sufficiently fast (total time) loop.

[Fangjun Jiang]

I don't see a rate limit. It definitely can update much faster than every second. I've had waitbar progress continuously as fast as you pour coffee to a cup.

On the other side, it can not be due to that the OP's loop is too fast. Run the bare waitbar() below will see a nice progress.

%%

h=waitbar(0,'progress');

for k=1:1000

waitbar(k/1000,h);

end

Answer 2

[Daniele Finazzi]

This question is quite old, but since I have recently had the same issue, here is how I fixed it.

My guess is that Matlab performs an integer division in the first argument of the waitbar, which then results in either 0 (0%) or 1 (100%). In my case, I displayed the percent progress on the waitbar like this (using the code above as an example):

waitbar(p / Total_pulse_Count, hwb, sprintf('%d%%', p*100/Total_pulse_Count));

and I noticed the bar was on 0 until 50% was reached, and after that it jumped straight to "full scale".

So I just forced the division inside the waitbar function to be non-integer:

waitbar(double(p) / double(Total_pulse_Count), hwb);

What I don't know is why this happens in some cases only. Up until now I had been using the waitbar in the same way without ever running into this issue.