random_array.poisson(0) gives -1 and -2
Hi, the random_array poisson functions returns negative values if mean=0:
from numarray import random_array as ra ra.seed(x=1, y=1) ra.poisson(0) 5 ra.poisson(0) -2
My "math book" tells me that it should be always zero. This seems to be a constructed case, but I'm using this to put "quantum statistic" into a simulated image: obj = na.array( something ) imageFromDetector = ra.poisson( obj ) + gaussianNoiseArray The object array might have lots of zeros surrounding the "actual object". Thinking of a fluorescent object sending out photons it makes sense to not get any photons at all from 'empty' regions. I'm using numarray 0.8; Thanks for numarray, Sebastian Haase
On Wed, 2004-05-19 at 14:25, Sebastian Haase wrote:
Hi, the random_array poisson functions returns negative values if mean=0:
from numarray import random_array as ra ra.seed(x=1, y=1) ra.poisson(0) 5 ra.poisson(0) -2
My "math book" tells me that it should be always zero. This seems to be a constructed case, but I'm using this to put "quantum statistic" into a simulated image: obj = na.array( something ) imageFromDetector = ra.poisson( obj ) + gaussianNoiseArray The object array might have lots of zeros surrounding the "actual object". Thinking of a fluorescent object sending out photons it makes sense to not get any photons at all from 'empty' regions. I'm using numarray 0.8;
I tried this on Fedora-1 i386 with Python-2.3.3 and it returned zero consistently. What platform are you on? Regards, Todd
On Wednesday 19 May 2004 12:03 pm, you wrote:
On Wed, 2004-05-19 at 14:25, Sebastian Haase wrote:
Hi,
the random_array poisson functions returns negative values if mean=0:
from numarray import random_array as ra ra.seed(x=1, y=1) ra.poisson(0)
5
ra.poisson(0)
-2
My "math book" tells me that it should be always zero. This seems to be a constructed case, but I'm using this to put "quantum statistic" into a simulated image: obj = na.array( something ) imageFromDetector = ra.poisson( obj ) + gaussianNoiseArray The object array might have lots of zeros surrounding the "actual object". Thinking of a fluorescent object sending out photons it makes sense to not get any photons at all from 'empty' regions. I'm using numarray 0.8;
I tried this on Fedora-1 i386 with Python-2.3.3 and it returned zero consistently. What platform are you on?
Regards, Todd
I running debian (Woody) $ uname -a Linux baboon 2.4.18 #1 Tue Dec 16 14:11:01 PST 2003 i686 unknown $python -v <snip> Python 2.2.1 (#1, Feb 28 2004, 00:52:10) [GCC 2.95.4 20011002 (Debian prerelease)] on linux2 and I get this:
ra.poisson(0, 100000).min() -4 ra.poisson(0, 100000).min() -4 ra.poisson(0, 100000).mean() 1.9383 ra.poisson(0, 100000).mean() 1.9607 ra.poisson(0, 100000).max() 29 ra.poisson(0, 100000).max() 28
Thanks for checking, Sebastian
participants (2)
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Sebastian Haase -
Todd Miller