On 04/06/2015 3:59 AM, Thierry Onkelinx wrote:
Dear Duncan,
I had been thinking about FAQ 7.31. I tried to create a dummy dataset
with the same structure to replicate the problem with the need of
sending my dataset. However all of them gave identical() results between
32-bit and 64-bit. Note that coef()$fRow is a 1266 x 6 data.frame. Is it
correct to infer that tiny difference between 32-bit and 64-bit are
possible but have a low probability of occurring?
Differences are rare, but it's hard to assign a probability to them.
Duncan Murdoch
signif() makes indeed more sense than round(). Using 20 digits gives
identical results, 21 digits gives non identical results.
Best regards,
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature
and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
To call in the statistician after the experiment is done may be no more
than asking him to perform a post-mortem examination: he may be able to
say what the experiment died of. ~ Sir Ronald Aylmer Fisher
The plural of anecdote is not data. ~ Roger Brinner
The combination of some data and an aching desire for an answer does not
ensure that a reasonable answer can be extracted from a given body of
data. ~ John Tukey
2015-06-03 18:09 GMT+02:00 Duncan Murdoch <murdoch.duncan at gmail.com
<mailto:murdoch.duncan at gmail.com>>:
On 03/06/2015 11:56 AM, Thierry Onkelinx wrote:
> Dear all,
>
> I'm a bit puzzled by the difference in an object when created in R
> and R 64-bit.
>
> Consider the code below. test.rda is available at
>
>
> # Run in R 3.2.0 Windows 32-bit, lme4 1.1-8
> library(lme4)
> load("test.rda")
> coef.32 <- coef(test)
> save(coef.32, file = "32bit.rda")
>
> # Run in R 3.2.0 Windows 64-bit, lme4 1.1-8
> library(lme4)
> load("~/test.rda")
> coef.64 <- coef(test)
> save(coef.64, file = "64bit.rda")
>
>
> # Compare the results
> # Run in R 3.2.0 Windows 32-bit, lme4 1.1-8
> # Run in R 3.2.0 Windows 64-bit, lme4 1.1-8
> library(lme4)
> load("32bit.rda")
> load("64bit.rda")
> identical(coef.32, coef.64) # FALSE
> identical(coef.32$fRow, coef.64$fRow) # FALSE
> identical(coef.32$fLocation, coef.64$fLocation) # TRUE
> identical(coef.32$fSubLocation, coef.64$fSubLocation) # TRUE
>
> The first comparison is FALSE, because the second is FALSE. But
> second FALSE and the third and fourth TRUE?
>
> My goal is the calculate a SHA1 hash on the coef(test) to track if
> coefficients of test have changed. I'd like to get the same hash
> 32-bit and 64-bit system. A simple hack would be to calculate the
> round(coef(test), 20). Is that a good or bad idea?
>
> identical(round(coef.32$fRow, 20), round(coef.64$fRow, 20)) # TRUE
Different math libraries round differently, so small differences are
expected. This is FAQ 7.31. In many cases the 32 bit calculations
more accurate, because they tend to use more 80 bit extended
intermediate values, but that is not guaranteed.
Rounding before comparing makes sense, but I would use signif()
of round(), I would choose a relatively small number of significant
digits, and I would expect to see a few false positives: if the true
value is 0 but some "random" noise is added, I'd expect values
by signif() to be unequal.
Duncan Murdoch
>
> Best regards,
>
> ir. Thierry Onkelinx
> Instituut voor natuur- en bosonderzoek / Research Institute for
> Forest
> team Biometrie & Kwaliteitszorg / team Biometrics & Quality
> Kliniekstraat 25
> 1070 Anderlecht
> Belgium
>
> To call in the statistician after the experiment is done may be no
> than asking him to perform a post-mortem examination: he may be
> what the experiment died of. ~ Sir Ronald Aylmer Fisher
> The plural of anecdote is not data. ~ Roger Brinner
> The combination of some data and an aching desire for an answer
> ensure that a reasonable answer can be extracted from a given body
> ~ John Tukey
>
> [[alternative HTML version deleted]]
>
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