How to add a x-axis line to a figure? (matlab)

Question

I want to add a x-axis line at 0 to a Matlab figure so that I can compare my data to see if it is positive or negative when saving the figures to a jpg. What is the best way to do this? I know you can use line() but it just seems cumbersome because you need to specify the x and the y ranges. Is there an easier way?

Paralysis

See https://mcmap.net/q/747479/-vertical-refline-in-matlab/7328782 for a similar question about vertical lines. – Muscolo

Possible duplicate of How to draw horizontal and vertical lines in MATLAB? – Dreary

Answer 1

I don't believe there is a built-in way that is more convenient. I use hline() and vline() from FileExchange, which work like a charm:

http://www.mathworks.com/matlabcentral/fileexchange/1039

Gelasias

Answer 2

There exist an undocumented function graph2d.constantline:

plot(-2:5, (-2:5).^2-1)

%# vertical line
hx = graph2d.constantline(0, 'LineStyle',':', 'Color',[.7 .7 .7]);
changedependvar(hx,'x');

%# horizontal line
hy = graph2d.constantline(0, 'Color',[.7 .7 .7]);
changedependvar(hy,'y');

The nice thing is that it internally implements a listener for the axes limits (handles change like pan, zoom, etc..). So the lines would appear to extend to infinity.

Celestinacelestine

Looks like my version of Matlab 7.0.1 R14 SP1 gives me a segmentation violation when I run your code and I don't get the x-axis line. :( – Paralysis

why the downvote, your version of MATLAB is pretty old, and as it turns out doesn't run the above solution.. Plus as I mentioned, this is an undocumented feature – Celestinacelestine

sorry, i didn't think it would do so. i tried to undo the upvote, but it caused the downvote instead. not very intuitive.. =/ now i can't do anything since the ans is locked until the post is edited and i don't have editing privileges. – Paralysis

Very nice solution! Exactly what i've been searching for a long time! – Wallache

update: unfortunately the function was removed in R2014b (which introduced the new HG2 graphics system). – Celestinacelestine

Answer 3

You could get this x range directly after the figure has been created. It goes a little something like this:

x=-2:5;
y=x.^2-1;

figure()
plot(x,y);

xlim = get(gca,'xlim');  %Get x range 
hold on
plot([xlim(1) xlim(2)],[0 0],'k')

Note that if you do any manual zooming out in the figure, the line might have to be redrawn to go over the entire new x range.

Kirstenkirsteni

Answer 4

A vline and hline command like in GNU R would be great, but I could not find a shorter solution than

plot(1:10,sin(1:10));
line(xlim,[0 0],'Color','r') 

Exerciser

This is a very elegant method! – Gearhart

Answer 5

1. Draw your data by plot() command or stem(). A figure window will open.
2. Then on the figure window, click on the [insert] command from the
   menu bar, a drop-down menu will appear.
3. From this menu click on the [line] command, now the shape of the
   cursor will change into a plus sign.
4. Now you can draw a line anywhere you want, either horizontal or
   vertical or slanted.
5. You can change the properties of line by right clicking on the
   line, a menu will appear from which you can choose your desires
   properties.
6. If you want to have some ticks on the line then you can use add text option, and place text where ever you want.
7. If you would like to have a code for your figure, click on [file] menu and then click on [generatecode] option, a new text editor
   window will open, you can save this code for further use. Good luck.

Armoured

Answer 6

Since MATLAB R2018b there is yline for this purpose:

 yline(0)

draws a horizontal line at y==0.

Muscolo