lme4 + R 2.11.0 + mac unavailable
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
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