# Why is probplot not plotting the reference line for one matrix column?

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Inputting a 1457x3 double matrix whose columns represent millimeter motion in 3D space, probplot is not plotting a reference line for the first column (lateral data). Why? (Removing this column, probplot works, so it appears limited to this data specifically.)

I have attached the DICOMallshifts data, the file created via csvwrite. Interestingly, WordPad is showing -0 whereas MATLAB simply has 0, (cf. screenshot below) ... Does this show that MATLAB is in fact treating the 0 as negative because of this line in my code redefining axes?

DICOMallshifts = cmtomm*...

[-InterfractionalElektaMotion(:,1) -InterfractionalElektaMotion(:,3) ...

InterfractionalElektaMotion(:,2)];

Are all the -0 data causing this error in probplot?

Here is the code generating the probplot figure:

figure

probplot(DICOMallshifts)

legend('show','Location','northwest')

Here is a screenshot showing the problem:

Discrepancy between MATLAB and data written to file:

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### Answers (1)

Massimo Zanetti
on 26 Jan 2017

##### 3 Comments

Massimo Zanetti
on 26 Jan 2017

Edited: Massimo Zanetti
on 26 Jan 2017

My suspect is that, having such a large number of same data (precisely many 0s) the line cannot be drawn because its angular coefficient is close to infinite (a vertical line cannot be defined as a function).

Inspect this:

x=linspace(0,1);

y=x*inf;

plot(x,y);

It throws no errors, but the line is not plotted.

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