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

josef.pktd@gmai... josef.pktd@gmai...
Sun Jun 13 16:25:03 CDT 2010


On Sun, Jun 13, 2010 at 5:20 PM, Robert Kern <robert.kern@gmail.com> wrote:
> On Sun, Jun 13, 2010 at 12:17, Vincent Davis <vincent@vincentdavis.net> wrote:
>>
>> On Sun, Jun 13, 2010 at 9:46 AM, Matthew Brett <matthew.brett@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).

It makes testing and bug-hunting a bit difficult if there are
different versions of numpy with the same version number.

Josef


>
> --
> 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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