Last modified: December 2018

URL: http://cxc.harvard.edu/sherpa/ahelp/poisson.html
AHELP for CIAO 4.11 Sherpa v1

poisson

Context: models

Synopsis

One-dimensional Poisson function.

Syntax

poisson

Description

A model expressing the ratio of two Poisson distributions of mean mu, one for which the random variable is x, and the other for which the random variable is equal to mu itself.


Example

>>> create_model_component("poisson", "mdl")
>>> print(mdl)

Create a component of the poisson model and display its default parameters. The output is:

mdl
   Param        Type          Value          Min          Max      Units
   -----        ----          -----          ---          ---      -----
   mdl.mean     thawed            1        1e-05  3.40282e+38           
   mdl.ampl     thawed            1 -3.40282e+38  3.40282e+38           

ATTRIBUTES

The attributes for this object are:

mean

The mean of the first distribution.

ampl

The amplitude of the model.

Notes

The functional form of the model for points is:

f(x) = ampl * mean! exp((x - mean) * log(mean)) / x!

The grid version is evaluated by numerically intgerating the function over each bin using a non-adaptive Gauss-Kronrod scheme suited for smooth functions [1] , falling over to a simple trapezoid scheme if this fails.

References


Bugs

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.