[Numpy-discussion] Numpy.linalg.eig oddity

Robert Kern robert.kern@gmail....
Wed Jun 23 16:17:27 CDT 2010

On Wed, Jun 23, 2010 at 13:25, Salim, Fadhley (CA-CIB)
<fadhley.salim@ca-cib.com> wrote:
> I've been investigating a truly bizarre bug related to the use of
> numpy.linalg.eig.
> I have two classes which both use numpy.linalg.eig. These classes are
> used at very different times and are not connected in any way other than
> the fact that they both share this particular dependancy.
> I have found that whichever class is called second will produce a
> slightly different answer if numpy.linalg.eig is used sometime earlier.
> I've eliminated all other variables besides the call to eig(). This
> seems completely implausible, and yet I have the data.
> As far as I am aware, eig() is wholly stateless and therefore using it
> should not affect any subsequent calls to the function, right?
> Numpy==1.2.1, Scipy==0.7.0
> I've checked the bug-trac for this function and can find no references
> to bugs which cause it to hold-state, even in the somewhat out of date
> version of numpy. Can somebody let me know if there's something that I'm
> missing.

I don't think we've seen anything like that before. If you can come up
with a small, self-contained script that demonstrates the problem, we
will take a look at it.

Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco

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