How to access displayed axis limits when scaling is logarithmic and data partly negative?

Hi,

I plot data. Some of the data are quite noisy and occasionally negative values appear, but I'm not interested in them. I apply a logarithmic y-axis scaling. Matlab issues a warning, that 'Negative data are ignored'. I use axis tight which adjusts the axes limits so that the displayed data (i.e. only the positive data!) just fit into the axes.

Now here's my question: How can I access the displayed y-limits?

get(axes_handle, 'YLim') returns the limits of all the data (positive and negative), so that the upper limit matches the displayed upper limit but the lower limit (negative) does not!

Here's a small example:

figure;
data = [-1 10 100 1000];
plot(data);
set(gca,'YScale','log');
axis tight;
ylim

The displayed y-limits are [10 1000] but ylim returns [-1 1000].

Anyone know a solution?

Stephan.

Answer 1

[Matt Tearle]

A hack would be to use the YTick values instead, as there's always a tick at the top and the bottom by default.

yl = get(gca,'YTick');
yl = yl([1,end])

[Stephan Heise]

Good idea!

Thanks Matt.

Answer 2

[C.J. Harris]

After you set 'axis tight' call the following commmand:

set(gca, 'YLimMode', 'auto')

Then 'ylim' should return:

[10 1000]

[Stephan Heise]

Thanks for the hint, Chris. If |YLimMode| is |auto| , |ylim| is indeed returned correctly. A drawback of this workaround is that the axis may not be "tight" after setting |YLimMode| to |auto|.