[Numpy-discussion] Bug or feature?
Sune Rastad Bahn
bahn at atomistix.com
Thu Nov 10 01:53:15 EST 2005
Thanks a lot for a very nice and extremely useful python module.
I recommend all my colleagues to try you package whenever they ask for a
matlab like environment. This week one of these friends came by me with an
oddity relating to the RandomArray module.
try the following on your linux command prompt:
do python -c "from RandomArray import *;seed();print randint(100000)";
and check the output. I get a steadily but slowly decreasing series of
According to the documentation seed() should initiatilize from the system
clock. If one checks the seed (using get_seed) it turns out to be the case
indeed, but that it is only very slowly changing (once a second), and only on
the second seed. e.g
python -c "from RandomArray import *;seed();print get_seed()"
My best guess is that this is the cause for the behavior seen above.
This could be filed as a feature, but I believe it is not the behavior people
would expect. At least the documentation should emphasize
that two runs started within a short time ( upto 1s) will give the exact same
result (experts on pseudo random numbers will know this, but the length of
the time 1sec is surprisingly long).
that the first random number is slowly varying (strongly correlated) with time
(this is more surprising). One fix is to take one randomnumber and throw
away, since the second number is not correlated with time (except from noted
Software Application Manager
Sune Rastad Bahn
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Mobile: +45 23 455 997
Email: bahn at atomistix.com
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