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

[Oleg Komarov]

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

[Bradley Stiritz]

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

[Oleg Komarov]

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

Answer 1

[Jan]

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]

[Bradley Stiritz]

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

[Yair Altman]

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

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

[Bradley Stiritz]

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

Answer 2

[Image Analyst]

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();

[Bradley Stiritz]

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

[Image Analyst]

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