[Numpy-discussion] Different results from repeated calculation

Keith Goodman kwgoodman at gmail.com
Mon Jan 29 17:00:20 EST 2007

On 1/29/07, Robert Kern <robert.kern at gmail.com> wrote:
> Keith Goodman wrote:
> > Here's a unit test for the problem. I am distributing it in hopes of
> > raising awareness of the problem. (What color should I make the
> > Repeatability Wristbands?)
> >
> > I am sure others are having this problem without even knowing it.
> Another datapoint using atlas3-base on Ubuntu AMD-64. Looking at the source
> package, I think it sets ISAEXT="sse2" for AMD-64 when building.
> rkern at rkernx2:~$ python repeat_test.py
> repeatability #1 ... ok
> repeatability #2 ... ok
> repeatability #3 ... ok
> ----------------------------------------------------------------------
> Ran 3 tests in 0.043s
> OK

I ported the test to octave which like numpy uses Atlas. On my machine
(debian etch atlas3-sse2) I get the problem in numpy but not in

Plus test1 always passes. So it is only when you reload x and y that
the problem occurs. If you load x and y once (test1) and repeat the
calculation, there is no problem.

Do these two results point, however weakly, away from atlas?

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