Re: [R] accuracy of test cases

From: Uwe Ligges <ligges_at_statistik.uni-dortmund.de>
Date: Fri 29 Apr 2005 - 21:27:40 EST

Robin Hankin wrote:

>
> On Apr 29, 2005, at 11:51 am, Uwe Ligges wrote:
>

>> Robin Hankin wrote:

>
>
> [snip]
>
>>> The tolerance should be as small as possible, but If I make it too 
>>> small, the test may fail
>>> when executed on a machine with different architecture from mine.
>>> How do I deal with this?
>>
>>
>> See ?all.equal
>>
>> Uwe Ligges
>>

>
> Hi Uwe
>
> Thanks for this. But sometimes my tests fail (right at the edge of a
> very wibbly wobbly
> function's domain, for example) even with all.equal()'s default tolerance.
>
> Maybe I should only include tests where all.equal() passes
> "comfortably" on my
> machine, and have done with it. Yes, this is the way to think about it: I
> was carrying out tests where one might
> expect them to fail (entrapment?). My mistake was to focus on the
> magnitude of
> "tol" and to blithely include tests where all.equal() failed, or came
> close to failing.
>
> Unfortunately, all the interesting stuff happens at the boundary.
>
> I guess (thinking about it again) that in such circumstances, there is
> no generic answer.

[We might want to move to R-devel for further discussion...]

Yes, of course the cases at the boundary are the interesting ones. Unfortunately, it is extremely hard (even if underlying algorithms are known - and if possible at all) to calculate the "expected" inaccuracy, if algorithms are becoming quite complex.

It would also be possible to intentional include a test that gives differences - don't know what Kurt et al. think about it (if we are talking about a CRAN package), though.

Best,
Uwe

>
> best wishes
>
> rksh
>
>
>
>
>
> --
> Robin Hankin
> Uncertainty Analyst
> Southampton Oceanography Centre
> European Way, Southampton SO14 3ZH, UK
> tel 023-8059-7743



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