Yes sure. I am making the required changes and will submit the patch again.
Thank you for your suggestions.

Yes, exactly Matlab is not creating a static line graphics object.
I have tried to mimic tis behaviour.

What I did is that I created dynamically changing vertical line. The vertical line length change according to the user needs. I have shown this in the images in the GNU discourse group. The discussion is going on there.

An initial implementation would be great, and then we can improve things from there.  This is not a difficult Octave project, but neither is it a trivial one.

The issue is that Matlab is not creating a static "line" graphics object.  Instead, they have created a new fundamental graphics type called "constantline".  In Octave, we can mimic that behavior by creating an hggroup object and then using addproperties() to create the properties that are missing from an ordinary line object.  A good example to build from is area.m in scripts/plot/draw directory.

The other tricky thing is that "constantline" is a dynamic object.  If the axis is resized then the underlying line object needs to have the data points changed so it again occupies the entire plot.  This is entirely feasible, but a little tricky.  When the hggroup is being built you will also need to use the addlistener() function to watch the current axes' "xlim" property (for a yline object).  The listener function will be a callback that adjusts the data in the line object to match the new xlimits.

Sample code for testing

yl = yline (2);  # Create yline at y==2, default xlimits of [0, 1]
xlim ([-5, 5]);

The above code should display a line that is now 10 data units long.

But, if you just want to get started and provide an initial implementation we can refine it from there.

@Tamandeep: You could check with the Matlab help page, if your code does (mostly) the same thing as Matlab does ( https://de.mathworks.com/help/matlab/ref/xline.html ) Ideally it would also generate (and return) the same type of graphics objects as Matlab does.

Hello everyone.
I have implemented xline and yline functions which are not in Octave,
The implemented function does the following
it takes a value input and creates a constant vertical line at that x coordinate for xline
similarly it goes for y line
I have also added linespec feature in this also for the specified line style, marker, and color.
I have also added a feature in which we can give x coordinates as a vector so that we can draw multiple vertical lines in xline

ping @rik to see if he has these lying around that someone could turn into at least partial compatibility hacks. if not we could at least make a quick missing_functions add.

Interesting, I wrote m-files to do this when I first started using Octave more than 10 years ago, but I called my files hline.m (horizontal line) and vline.m (vertical line).  I can dust them off and add them to Octave.