[Scipy-tickets] [SciPy] #1883: No non-positive parameter values accepted for non-central t-distributions

SciPy Trac scipy-tickets@scipy....
Fri Mar 29 11:00:44 CDT 2013


#1883: No non-positive parameter values accepted for non-central t-distributions
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 Reporter:  Sytse   |       Owner:  somebody   
     Type:  defect  |      Status:  new        
 Priority:  normal  |   Milestone:  Unscheduled
Component:  Other   |     Version:  0.11.0     
 Keywords:          |  
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 The non-central t-distribution in scipy.stats.distributions accepts a non-
 centrality parameter with positive values only.

 From Wikipedia (http://en.wikipedia.org/wiki/Noncentral_t-distribution):
 "If Z is a normally distributed random variable with unit variance and
 zero mean, and V is a Chi-squared distributed random variable with ν
 degrees of freedom that is statistically independent of Z, then
 T=(Z+μ)/sqrt(V/ν) is a noncentral t-distributed random variable with ν
 degrees of freedom and noncentrality parameter μ. Note that the
 noncentrality parameter may be negative."

 Adding a function:[[BR]]

 def _argcheck(self, df, nc):[[BR]]
      return (df > 0)[[BR]]

 to the class class nct_gen  would completely solve the problem.

-- 
Ticket URL: <http://projects.scipy.org/scipy/ticket/1883>
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