axis changes even after "axis equal"

I would like to plot a line on an axis without changing the XLim and YLim values. I obviously went through the "axis equal" command (or the ax.XLimMode='manual'; ax.YLimMode='manual';) but this doesn't seems to work.

Where am I doing wrong?

 plot(1:10)
 % XLim is not [1 10]
 axis manual
 plot(1:20)
 % XLim should be again [1 10], instead it's [0 20] now

it works with

 plot(1:10)
 % XLim is not [1 10]
 hold on
 axis manual
 plot(1:20)
 % XLim should be again [1 10], instead it's [0 20] now

but I don't want to hold previous plots (it's an animation).

A workaround could be to use

 ph=plot(1:10)
 axis manual
 hold on
 delete(ph)
 plot(1:20)

but I this seems over-complicated to do the simple thing I'm asking to...

I'm working with matlab R2015a

Answer 1

[Chad Greene]

If you don't hold the plots, axis limits will be reset every time you call plot. For an animation, you can use hold and either delete plotted objects or change their data. That is,

hold on
h = plot(1:10); 
<grab animation frame here>
delete(h) 
h = plot(1:20);

and so on. Or you can change the data in h with

set(h,'xdata',1:20,'ydata',1:20)

[Luca Amerio]

Yes, I already though to both these solutions. Was hoping for a simpler one because I need to teach this to students that are not familiar with MATLAB.

Using delete, set of h.XData=[...] are adding a further complication to a simple problem.

To bad: I was hoping the solution to be cleaner.

Answer 2

[pfb]

If I understand this correctly, you want an animation with fixed xlim, but you do not want to set the xdata and ydata (I agree with Chad Greene that this is the way to go, but I understand your commment about your students).

I guess that you're plotting plots in a loop, to form the animation. So why not setting the desired xlim after each plot, instead of holding it and deleting it?

It is not optimal, but it should not make much difference if you're grabbing frames for a movie.

If you are just "showing" a movie, it won't look very good, though. Maybe you can pause the loop for a tiny while after each xlim. I think you need also drawnow.

 figure(1)
 clf
 for n=1:10
     plot(1:10,(1:10)*n);
     axis([1 10 1 100]);
     drawnow;
     pause(.2); %change this according to your needs
 end

[Luca Amerio]

Thank you very much. This could be a doable workaround. I will decide if either this or delete(h) cause less questions.

Thank you very much.

[pfb]

You're welcome. But I think you accepted the other answer :)