[Scipy-tickets] [SciPy] #1647: BUG: stats: _argcheck function for the erlang distribution is misnamed.

SciPy Trac scipy-tickets@scipy....
Sat May 5 14:21:37 CDT 2012


#1647: BUG: stats: _argcheck function for the erlang distribution is misnamed.
------------------------------+---------------------------------------------
 Reporter:  warren.weckesser  |       Owner:  somebody    
     Type:  defect            |      Status:  needs_review
 Priority:  normal            |   Milestone:  Unscheduled 
Component:  scipy.stats       |     Version:  0.10.0      
 Keywords:                    |  
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Comment(by josefpktd):

 about fit. My guess (!) is that if the function is nicely behaved, then
 using continuous optimization (with low precision for convergence of
 parameters) should be faster than integer search without good starting
 values.

 Just rounding the shape parameter won't be enough, because we would have
 to reestimate loc and scale (if they are not fixed) with the rounded
 parameter, and most likely have to check both sides (floor and ceil).

 What I tried to explain with the example of fitting the t distribution,
 is, that I don't know if someone would want this. The first time I was
 fitting the t-distribution with another package, I was surprised to get a
 float, non-integer valued estimate for the shape (degrees of freedom). But
 if we look at it just as a heavy tailed distribution, then there is no
 reason to look only at integer degrees of freedom. Even in statistics we
 have in some cases fractional dof.

 The erlang case is a bit different because it is essentially a duplicate
 of gama, so imposing integer values wouldn't prevent users from estimating
 the same distribution with continuous parameter values.

-- 
Ticket URL: <http://projects.scipy.org/scipy/ticket/1647#comment:10>
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