Odd behaviour when displaying fit results in UIAxes in App Designer (Matlab R2023b)

Hi,

I am currently working on an app in the app designer and I keep having odd behaviour when displaying my fit results in the UIAxes of my app.

When I press the fit button, the fit is displayed as expected.

When I click the button again the fit is extended:

This is the code I use:

yData and xData are vectors of the size 200x1 each.

% Button pushed function: FitButton
        function FitButtonPushed(app, event)
            [~, locs, w, ~] = findpeaks(app.yData,app.xData,'Threshold',app.threshold);
            app.smoothFit = fit(app.xData,app.yData,'smoothingspline');
            

            % determine height
            hgt = zeros(length(locs), 1);
            for k = 1:length(locs)
	            hgt(k) = feval(app.smoothFit,locs(k));
            end

            app.x = linspace(app.xData(20),app.xData(end),100000);

            for n = 1:length(locs)
	            Gauss(n,:) = hgt(n)*exp(-((app.x - locs(n))/w(n)).^2);
            end

            plot(app.UIAxesFit,app.smoothFit)
            hold(app.UIAxesFit, 'on')
            plot(app.UIAxesFit,app.x,Gauss,'--')
            legend(app.UIAxesFit,'off')
            xlabel(app.UIAxesFit,'CCS (Ų)')
            ylabel(app.UIAxesFit,'Intensity')
            hold(app.UIAxesFit, 'off')

        end

I would be greatful for suggestions on why this is happening.

Thanks!

Silvana

[Adam Danz]

It looks like the limits on the x-axis is expanded on the second fit to include a datapoint to the left around (-200,-1.8) and extends to the right to around (1200,0). Data between x=100 to x=900 appears to be the same between the two images.

Why is this happening?

I would start that investigation by confirming that the app.xData and app.yData isn't changing between calls to FitButtonPushed. If those data do not change, I would look into how localFit changes between calls to FitButtonPushed. This is assuming the red line is produced by plot(app.UIAxesFit,localFit).

Workaround

Setting xlim([100,900]) or whatever range of x-values you expect should result in auto rescaling of the axis so the second plot appear similar to the first plot. However, that doesn't answer why this is happening and that's worth investigating.

[SilvanaZ]

Hi Adam,

thank you for your answer. :-)

Unfortunatly, there is no data point at (-200,-1.8) in my data. This seem to be an artefact of the fit. (If I call FitButtonPushed again, a new point will appear. the red line produced by plot(app.UIAxesFit,localFit) will continue to expand.)

app.xData and app.yData should be the same every time I press the button. They are the input data and they are defined earlier on. I will double check to make sure, however.

I agree with your workaround. This would at least make it look the same. But it is just soooo strange that this artifical "expansion" of the fit happens...

I will keep this question open, maybe someone else has an idea.

[Jon]

Would it be possible for you to attach your app, or a simplified version of the app, that reproduces the problem behavior. It would be helpful for me (and probably for you) to be able to step through the code with the debugger to see exactly what is going on.

[SilvanaZ]

Hi Jon,

This is my app file. Please keep in mind that it is not totally finished yet.

(I am still learning how to code in Matlab and in general, so nothing is perfect)

I have also added an input file you can use.

Thanks for taking the time :)

[Adam Danz]

Given the app and data, what are the instructions to recreate the problem?

[SilvanaZ]

Hi Adam,

please save the inputForApp file to your computer. Copy its path via right click "Copy as Path". (I am working on a Windows computer, copying the path this way surrounds the file location with this symbol "filepath". the dividing symbol is the backslash \. )

You enter this into the text box: File Path to Results Table. Then press the Read Table button.

Then you press the IMMS1 button, select the threshold (0.0016) and then press the fit button once: This should result in the graph seen in the first picture. Then just keep on pressing the fit button as often as you want. You should be able to see the plot of the fit expand (like in the second picture).

I hope this works for you too. Let me know if there are any other questions.

[Jon]

I'm assuming that your fit function is from the Curve Fitting Toolbox. Unfortunately I don't have that toolbox, so I can not run your example.

Answer 1

[Adam Danz]

When plotting a cfit object using plot(ax,cfit) the x-values for the line are selected based on the axes limits. Every time you run the FitButtonPushed callback function, the axes limits slightly expand. Therefore, the extent of the fit line also expands.

To prevent this from happening, freeze the XLim values prior to plotting the lines.

Option 1

This sets the XLimMode to manual which freezes the X-limits.

% Add this line
app.UIAxesFit.XLimMode = 'manual'; 

plot(app.UIAxesFit,localFit)

Option 2

This also sets the XLimMode to manual which freezes the X-limits but returns the original XLimMode values after the callback is complete.

% Add these two lines
restoreXLimMode = onCleanup(@()set(app.UIAxesFit,'XLimMode',app.UIAxesFit.XLimMode));
app.UIAxesFit.XLimMode = 'manual'; 

plot(app.UIAxesFit,localFit)

[SilvanaZ]

Dear Adam,

thank you for this answer.

I am not sure why the x-values would be selected based on the axes limits (in my mind this makes no sense...) but both options work.

I will accept the answer, because it fixes my issue for the time being. I just want to point out that when I zoom out in the figure the original issue persists (which makes sense).

Thank you for your help! This has saved me a lot of time :-)

BR

Silvana