[R-SIG-Mac] [R] lme4 + R 2.11.0 + mac unavailable

[Martin Maechler]

On Sat, Jul 31, 2010 at 04:25, John Maindonald
<john.maindonald at anu.edu.au> wrote:
> Is optimisation of code a possibility, i.e., the same algebraic calculations
> done  in a slightly different way depending on the state of various registers?

I'm really not a Mac specialist and neither one in those low level
system / CPU computations,  but indeed, exactly something like that
has been my current guess about what's happening...

> E.g., (ab)c vs a(bc), but it would almost certainly be more subtle than that.
yes, more subtle ( I hope).  We know that computer arithmetic does
*not*  fulfill most of these basic arithmetic laws, but remember that
here, we cannot imagine how the numeric matrices that are used in the
computations could *start*  differently, and then I'd wonder how
differences came about...
and recall that the differences we've seen where not just in the last
few significant bits

> That seems to me the sort of thing that is likely to be Mac-specific.

interesting...  so you have seen other evidence of such behavior?

>
> John Maindonald             email: john.maindonald at anu.edu.au
> phone : +61 2 (6125)3473    fax  : +61 2(6125)5549
> Centre for Mathematics & Its Applications, Room 1194,
> John Dedman Mathematical Sciences Building (Building 27)
> Australian National University, Canberra ACT 0200.
> http://www.maths.anu.edu.au/~johnm
>
> On 31/07/2010, at 5:09 AM, Martin Maechler wrote:
>
>> On Fri, Jul 30, 2010 at 17:29, Simon Urbanek
>> <simon.urbanek at r-project.org> wrote:
>>>
>>> On Jul 29, 2010, at 7:51 PM, Martin Maechler wrote:
>>>
>>>>>>>>> "KB" == Ken Beath <ken at kjbeath.com.au>
>>>>>>>>>   on Wed, 28 Jul 2010 01:19:34 -0000 (GMT) writes:
>>>>
>>>>   KB> On Tue, July 27, 2010 11:07 pm, John Maindonald wrote:
>>>>>> Binaries for lme4 are not for the time being available either on
>>>>>> CRAN or on r-forge?
>>>>>>
>>>>
>>>>   KB> There was a discussion about this on R-Sig-ME. It fails one of the checks
>>>>   KB> on the machine used to build the mac packages. It may pass on machines
>>>>   KB> with a later version of MacOS, but there didn't seem to be a consensus of
>>>>   KB> whether failing the checks was a problem.
>>>>
>>>> The underlyign issue seems to remain unresolved.
>>>> My best guess is still to low-level bugs somewhere in the libraries
>>>> used.
>>>>
>>>> However, to help users,
>>>> I'm willing to *not* run those tests when *running* on the Mac.
>>>>
>>>> What does
>>>>    Sys.info()[["sysname"]]
>>>>
>>>> return on the Mac, i.e., different versions of R running on the
>>>> Mac?
>>>> From grepping around I'd expect it give  "Darwin"  in all cases.
>>>> Is that true?
>>>>
>>>
>>> ... why don't you just compare the values with tolerance? That seems to make more sense that to disable the test altogether ...
>>>
>>
>> Doug and I have explained in several occasions (but maybe not on R-SIG-Mac)
>> that this is *NOT* the point here.
>> It's not about "basically the same computations" it's about
>> identical computations, i.e. from identical numerical matrices and so
>> the use of identical() has been very much on purpose, and is different
>> from the well justified typical use of
>> all.equal() which we use in many other places.
>>
>> And what people where reporting *is* a bit disturbing: The same
>> computations giving different answers for *exactly* the same
>> computation, e.g., depending if they had used
>> library(lme4)  or  require(lme4)  to load the package ...
>> and the difference was not just the last significant bit, but changes
>> at about the 7-th significant digit.
>>
>> Martin
>>
>>
>>> Cheers,
>>> Simon
>>>
>>
>> _______________________________________________
>> R-SIG-Mac mailing list
>> R-SIG-Mac at stat.math.ethz.ch
>> https://stat.ethz.ch/mailman/listinfo/r-sig-mac
>
>