[issue30464] gammavariate has a wrong comment

[Leonardo De Marchi]

New submission from Leonardo De Marchi:

The gammavariate function in random.py has a wrong comment.

It says that when alpha is one it's equivalent to call expovariate(1).

We can see that is not true (see graphs) and it should be expovariate(1/beta). 
It's not a big deal but it can cause confusion.

--
files: unnamed.png
messages: 294403
nosy: leodema
priority: normal
severity: normal
status: open
title: gammavariate has a wrong comment
Added file: http://bugs.python.org/file46895/unnamed.png

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[issue30464] gammavariate has a wrong comment

[Leonardo De Marchi]

Changes by Leonardo De Marchi :


--
pull_requests: +1896

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[issue30561] sync-up gammavariate and expovariate code

[Leonardo De Marchi]

New submission from Leonardo De Marchi:

As suggested by rhettinger in http://bugs.python.org/msg294438:

I agree that the comment should be changed. While we at it, perhaps sync-up 
with expovariate() code and eliminate the ``u <= 1e-7`` test:

Instead of:

elif alpha == 1.0:
# expovariate(1)
u = random()
while u <= 1e-7:
u = random()
return -_log(u) * beta

Use this instead:

elif alpha == 1.0:
# expovariate(1.0 / beta)
return -_log(1.0 - random()) * beta

--
messages: 295102
nosy: leodema
priority: normal
severity: normal
status: open
title: sync-up gammavariate and expovariate code
type: performance

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[issue30561] sync-up gammavariate and expovariate code

[Leonardo De Marchi]

Changes by Leonardo De Marchi :


--
pull_requests: +2011

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[issue30464] gammavariate has a wrong comment

[Leonardo De Marchi]

Changes by Leonardo De Marchi :


--
pull_requests: +2012

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[issue30561] sync-up gammavariate and expovariate code

[Leonardo De Marchi]

Changes by Leonardo De Marchi :


--
pull_requests: +2014

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