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?

Answer 1

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.

Answer 2

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.

Answer 3

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') 

Answer 4

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

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.

Answer 6

Since MATLAB R2018b there is yline for this purpose:

 yline(0)

draws a horizontal line at y==0.