[SciPy-dev] nbinom.ppf

josef.pktd@gmai... josef.pktd@gmai...
Sat Aug 1 10:29:59 CDT 2009


On Tue, Jul 28, 2009 at 12:56 PM, Robert Kern<robert.kern@gmail.com> wrote:
> On Mon, Jul 27, 2009 at 20:11, <josef.pktd@gmail.com> wrote:
>> That's better. It took me a while to understand the logic behind the
>> way the ceiling error is corrected. The same pattern is also followed
>> by the other discrete distributions that define a _ppf method. It is
>> cleaner then the epsilon correction, but takes longer to figure out
>> what it does.
>>
>> To understand the logic more easily and to be DRY, it would be better
>> to replace the duplication of the _cdf method directly with a call to
>> self._cdf.
>> For example, in changeset 4673, Robert, you changed the _cdf method to
>> use betainc instead of nbdtr, but not the _ppf method. Without the
>> code duplication, partial corrections could be more easily avoided.
>>
>> Is there a reason not to call self._cdf instead?
>
> Nope. Go ahead.
>
> --
> Robert Kern
>
> "I have come to believe that the whole world is an enigma, a harmless
> enigma that is made terrible by our own mad attempt to interpret it as
> though it had an underlying truth."
>  -- Umberto Eco
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for the record: dlaplace and boltzman also fail the roundtrip test

boltzmann (1.3999999999999999, 19)
[ 1.  2.  3.  3.]
[ 0.  1.  2.  3.]
False True False [ 0.  3.]
dlaplace (0.80000000000000004,)
[-5. -4. -3. -2. -1.  1.  1.  2.  3.  4.  5.]
[-5. -4. -3. -2. -1.  0.  1.  2.  3.  4.  5.]

Josef


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