[SciPy-User] Gamma distribution in scipy.stats

Bruce Southey bsouthey@gmail....
Thu Jan 28 13:07:45 CST 2010


On 01/28/2010 12:16 PM, josef.pktd@gmail.com wrote:
> On Thu, Jan 28, 2010 at 1:08 PM, Gökhan Sever<gokhansever@gmail.com>  wrote:
>    
>>
>> On Thu, Jan 28, 2010 at 11:50 AM, Robert Kern<robert.kern@gmail.com>  wrote:
>>      
>>> On Thu, Jan 28, 2010 at 11:36, Gökhan Sever<gokhansever@gmail.com>  wrote:
>>>        
>>>> Hello,
>>>>
>>>> Could someone explain to me why doesn't scipy explicitly use the
>>>> location
>>>> and scaling parameters representing its PDF?
>>>>          
>>> Because the transformation for the location and scale parameters are
>>> the same for every PDF and is well known. However, including them in
>>> the formula often clutters it up and obscures the differences between
>>> PDFs.
>>>
>>>        
>> GSL and R doesn't use the location parameter then. And Numpy's Gamma PDF
>> includes scaling in the formulae
>> (http://docs.scipy.org/doc/numpy/reference/generated/numpy.random.gamma.html#numpy.random.gamma).
>> I am guessing that everyone has its own style when it comes to represent the
>> distributions. Not so surprisingly it is shown in a different form in my
>> Cloud and Precipitation Parametrization book.
>>
>> I suggest to add a statement like: Gamma distribution is mainly used to
>> represent precipitation distribution in bulk cloud parametrization schemes.
>>      
> I don't think "mainly" is a correct description,
>
> a random quote after a short google search
> "The Gamma distribution is widely used in engineering, science, and
> business, to model continuous variables that are always positive and
> have skewed distributions"
>
> It's a pretty common distribution.
>
> Josef
>
>
>    
I think what  Gökhan is getting at is that limited description provided 
in the documentation link:
"The Gamma distribution is often used to model the times to failure of 
electronic components, and arises naturally in processes for which the 
waiting times between Poisson distributed events are relevant."

I actually think that part should be removed from the documentation.

Bruce




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