MATLAB Answers

Anomalous histogram for small argument

1 view (last 30 days)
Running the following code from the command line with c = 1e-15 or greater leads to a normal histogram
c = 1e-15; figure; histogram(c * rand(100,1))
Running the following code with c = 1e-16 or less leads to an incorrect histogram
c = 1e-16; figure; histogram(c * rand(100,1))
The problem appears also in apps when the histogram function is invoked.
Is this a bug?


Sign in to comment.

Accepted Answer

Bruno Luong
Bruno Luong on 7 Sep 2019
Edited: Bruno Luong on 7 Sep 2019
Yes it is a BUG. I chase back and in the file
C:\Program Files\MATLAB\R2019a\toolbox\matlab\datafun\+matlab\+internal\+math\binpicker.m
line #20 (R2019a)
there is a test
if xrange > max(sqrt(eps(xscale)), realmin(class(xscale)))
To me the correct test should be (without sqrt)
if xrange > max(eps(xscale), realmin(class(xscale)))
Now if I change this line and rerun the code
c = 1e-16; figure; histogram(c * rand(100,1))
it produces correct plot
More seriously, the function binpicker is called by HISTCOUNT. So HISTCOUNT is also buggy. Not only plotting but calculation might be wrong.

  1 Comment

Gordon Edwards
Gordon Edwards on 7 Sep 2019
Thanks for your reply.and I believe that you have spotted the error in function binpicker.Since eps(x) ~ 1e-16*x, and in my case xscale and xrange are nearly equal, the condition that
xrange > sqrt(eps(xscale))
leads to xrange >~ 1e-16 which is what I find.

Sign in to comment.

More Answers (1)

Jackson Burns
Jackson Burns on 7 Sep 2019
Here's a similar question asked a few years ago which was never really solved either. This comment may be your best approach, but I would reccomend just bringing the values to unity with something like this:
c = 1E-16;
mydata = c * rand(100,1);
You could then modify the xticklabels to match whatever the original values were.


Sign in to comment.




Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!