[Numpy-discussion] comparing floating point numbers
David Cournapeau
cournape@gmail....
Wed Jul 21 03:46:11 CDT 2010
On Tue, Jul 20, 2010 at 3:31 AM, Ondrej Certik <ondrej@certik.cz> wrote:
> Hi,
>
> I was always using something like
>
> abs(x-y) < eps
>
> or
>
> (abs(x-y) < eps).all()
>
> but today I needed to also make sure this works for larger numbers,
> where I need to compare relative errors, so I found this:
>
> http://www.cygnus-software.com/papers/comparingfloats/comparingfloats.htm
Actually, there is better, as mentioned in that same page. I
implemented the functions for reliable, amplitude independent floating
point comparison:
assert_array_max_ulp:
Given two arrays a and b, check that every item differs in at most N
Unit in the Last Place.
assert_array_almost_equal_nulp
Compare two arrays relatively to their spacing. It is a relatively
robust method to compare two arrays whose amplitude is variable.
Note
----
An assertion is raised if the following condition is not met:
abs(x - y) <= nulps * spacing(max(abs(x), abs(y)))
Parameters
----------
x: array_like
first input array
y: array_like
second input array
nulp: int
max number of unit in the last place for tolerance (see Note)
I think we should go toward using those almost everywhere we need
floating point comparison in testing,
cheers,
David
More information about the NumPy-Discussion
mailing list