[SciPy-user] scipy.special.erf randomly returns NANs on OSX

Robert Kern robert.kern at gmail.com
Sun Jan 22 20:15:50 CST 2006


Evan Monroig wrote:
> Hi,
> 
> I have this strange problem that the special erf function returns NANs
> when the input is an array:

> Can anyone reproduce the problem?

Yes, also on OS X, and only with the almost-but-not-quite-1.0 that you get by
adding 0.1 to 0.0 ten times.

In [9]: x = 0.0

In [10]: for i in range(10):
   ....:     x += 0.1
   ....:

In [11]: x
Out[11]: 0.99999999999999989

In [12]: scipy.special.erf(x)
Out[12]: nan

It's probably a platform-specific bug in Cephes. I'll try to see if it shows up
in C, too.

-- 
Robert Kern
robert.kern at gmail.com

"In the fields of hell where the grass grows high
 Are the graves of dreams allowed to die."
  -- Richard Harter



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