Re: [Numpy-discussion] problem with poisson generators

[Flavio C. <fcc...@gm...>]

2005/7/13, David M. Cooke <co...@ph...>:
>=20
> On Tue, Jul 12, 2005 at 05:32:25PM -0300, Flavio Coelho wrote:
> > Hi,
> >
> > I am having problems with the poisson random number generators of both
> > Numarray and Numeric.
> > I can't replicate it when calling the function from the python cosonle,=
=20
> but
> > it has consistently malfunctioned when used within one of my scripts.
> >
> > What happens is that it frequently return a value greater than zero whe=
n
> > called with zero mean: poisson(0.0)
> >
> > Unfortunately My program is too big to send attached but I have=20
> confirmed
> > the malfunction by printing both the mean and the result whenever it=20
> spits
> > out a wrong result.
> >
> > This is very weird indeed, I have run poisson millions of times by itse=
l=20
> on
> > the python console, without any problems...
> >
> > I hope it is some stupid mistake, but when I replace the poisson=20
> function
> > call within my program by the R equivalent command (rpois) via the rpy
> > wrapper, everything works just fine...
> >
> > any Ideas?
>=20
> This looks like bug #1123145 in Numeric:
>=20
>=20
> http://sourceforge.net/tracker/index.php?func=3Ddetail&aid=3D1123145&grou=
p_id=3D1369&atid=3D101369
>=20
> which was fixed a few months ago. numarray, I believe, originally took
> ranlib.c from Numeric, so it doesn't have this bug fix. Try replacing
> numarray's ranlib.c with the version from Numeric 24.0b2 (or CVS).



I have both numeric 23.7 and numarray 1.3.1 installed and on neither of the=
m=20
I could reproduce the bug when I called them directly from the python=20
interpreter. However they fail on mean 0.0 every time when called within my=
=20
code. So it appears to me that the Bug you mentioned is not what is causing=
=20
my problem. It seems to stem from interaction with the way its being called=
,=20
maybe some carryover from previous calls...
this is the test I ran on the interpreter:
[(poisson(i),i) for i in uniform(-20,20,1000) if i<=3D0]=20

I also ran:

sum(poisson(0,100000))

they both worked flawlessly. In the first test I wanted to see if there was=
=20
some carry over from previous runs when called with various means (which is=
=20
closer to the way it is used within my code), but it returned zero every=20
time. (I don't use negative means in my code, but I wanted to try it here=
=20
just in case)

--
> |>|\/|<
>=20
> /------------------------------------------------------------------------=
--\
> |David M. Cooke http://arbutus.physics.mcmaster.ca/dmc/
> |co...@ph... <http://physics.mcmaster.ca>
>=20



--=20
Fl=E1vio Code=E7o Coelho
registered Linux user # 386432
---------------------------
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