determine axis limits *before* plotting..?

Hi everyone,

I need to determine the y-axis limits "before" rendering my plot, b/c the elements are rendered in a loop, one at a time. xlim() isn't any use in this case. Will I have to reverse-engineer MATLAB's algorithm, or is there another approach?

Thanks, Brad

I don't understand your question. Can't you use xlim after the loop?

Hi Oleg,

Thanks for your question. Let me clarify: within the rendering loop, MATLAB is forced to reset the y-axis limits & re-render the whole plot each time a new figure element is drawn which exceeds the current limits. Doing this hundreds of times for a single plot is significantly time-consuming.

Therefore, as I said, I want to determine & set the y-axis limits via ylim() "before" the rendering loop. Does this make sense?

Thanks, Brad

I think we might help you if you posted the code.

Answer 1

Yair has explained some tricks to http://undocumentedmatlab.com/blog/plot-performance/. You can set the XLimMode of the current axes to 'fixed' and let Matlab determine the limits at the end only by resetting it to 'auto'.

[EDITED, link fixed, thanks Yair]

Jan, thanks, I this this might work for me. I'll test out & report back here.

The correct link is http://undocumentedmatlab.com/blog/plot-performance/

Also relevant: http://undocumentedmatlab.com/blog/plot-liminclude-properties/

Yair, thanks for the very helpful blog postings. Your work is greatly appreciated, as always!

Answer 2

You can save the y and x limits for the current axes at any time by using the ylim and xlim functions:

% Save initial limits.
initial_ylim_values = ylim();
initial_xlim_values = xlim();
% Now plot something that will change the ylimits
plot(x, y); % Some y that will change the y limits.
after_ylim_values = ylim();
after_xlim_values = xlim();

Hi, thanks for your comment. I'm not sure you're seeing my situation? Please see my response to Oleg, above..

Then you need to set "hold on" and MATLAB will "lock down" all those settings and not allow subsequent plots to change them.