[SciPy-Dev] seeded randn gets different values on osx

[Robert Kern]

On Sun, Jun 13, 2010 at 12:17, Vincent Davis <vincent at vincentdavis.net> wrote:
>
> On Sun, Jun 13, 2010 at 9:46 AM, Matthew Brett <matthew.brett at gmail.com> wrote:
>>
>> Hi,
>>
>> >> After a little discusion with Josef here are some results. It appears
>> >> to me that osx gets different values from a seeded randn
>> >
>> >> On my machine OSX py 2.6.5, numpy 1.4.0 scipy 8.0b
>> >>>>>> np.random.seed(0)
>> >>>>>> np.random.randn(3)
>> >>> array([ 0.06897149,  1.32078057,  1.5997924 ])
>>
>> Nor in a numpy-1.4.0 virtualenv:
>>
>> In [1]: import numpy as np
>>
>> In [2]: np.__version__
>> Out[2]: '1.4.0'
>>
>> In [3]: np.random.seed(0)
>>
>> In [4]: np.random.randn(3)
>> Out[4]: array([ 1.76405235,  0.40015721,  0.97873798])
>
> I just built 2.6 from current daily snapshot and installed numpy. Now I get the right answer
> MacBookPro-new-2:~ vmd$ py26
> Python 2.6.5+ (release26-maint, Jun 13 2010, 10:02:04)
> [GCC 4.2.1 (Apple Inc. build 5659)] on darwin
> Type "help", "copyright", "credits" or "license" for more information.
> >>> import numpy
> >>> import numpy as np
> >>> np.random.seed(0)
> >>> np.random.randn(3)
> array([ 1.76405235,  0.40015721,  0.97873798])
> So I guess there is something wrong with the enthought 6.2 dist.

It was an intentional, but poorly thought out change. Ilan Schnell
implemented a fast ziggurat algorithm for generating normal variates.
I think we will be reverting this modification for the stock numpy in
EPD (but don't quote me on that).

--
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