Randomness not due to seed

Hi,

Even using the same math libraries you can get different results,
depending on what sorts of instructions those libraries use, see the
following (none R related) blog article:
http://blog.nag.com/2011/02/wandering-precision.html.

Martyn

-----Original Message-----
From: r-devel-bounces at r-project.org
[mailto:r-devel-bounces at r-project.org] On Behalf Of Duncan Murdoch
Sent: 20 July 2011 14:47
To: Jeroen Ooms
Cc: r-devel at r-project.org
Subject: Re: [Rd] Randomness not due to seed

I would guess the error below is because of Java messing around in the
hardware.  It's pretty common on Windows for DLLs to attempt to change
the precision setting on the floating point processor; I hadn't seen
that before on Linux, but that would be my guess as to the cause.

It's also possible that one of the attached packages has messed with R
functions somehow, e.g. by replacing the default print() or show()
method.

A third possibility is that different math libraries are being used.

So I would consider the differences in the results to be a bit of a bug,

but not one that is likely under our control, and not one that is so
large that I would worry about working around it.

Duncan Murdoch

On 20/07/2011 8:03 AM, Jeroen Ooms wrote:

 >>   I think Bill Dunlap's answer addressed it:  the claim appears to

be false.

 Here is another example where there is randomness that is not due to
 the seed. On the same machine, the same R binary, but through another
 interface. First directly in the shell:

 >   sessionInfo()

 R version 2.13.1 (2011-07-08)
 Platform: i686-pc-linux-gnu (32-bit)

 locale:
   [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
   [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
   [5] LC_MONETARY=C              LC_MESSAGES=en_US.UTF-8
   [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
   [9] LC_ADDRESS=C               LC_TELEPHONE=C
 [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

 attached base packages:
 [1] stats     graphics  grDevices utils     datasets  methods   base

 >   set.seed(123)
 >   print(coef(lm(dist~speed, data=cars)),digits=22)

                (Intercept)                     speed
 -17.579094890510951643137   3.932408759124087715975



 # And this is through eclipse (java)

 >   sessionInfo()

 R version 2.13.1 (2011-07-08)
 Platform: i686-pc-linux-gnu (32-bit)

 locale:
   [1] LC_CTYPE=en_US.UTF-8          LC_NUMERIC=C
   [3] LC_TIME=en_US.UTF-8           LC_COLLATE=en_US.UTF-8
   [5] LC_MONETARY=en_US.UTF-8       LC_MESSAGES=en_US.UTF-8
   [7] LC_PAPER=en_US.UTF-8          LC_NAME=en_US.UTF-8
   [9] LC_ADDRESS=en_US.UTF-8        LC_TELEPHONE=en_US.UTF-8
 [11] LC_MEASUREMENT=en_US.UTF-8    LC_IDENTIFICATION=en_US.UTF-8

 attached base packages:
 [1] stats     graphics  grDevices utils     datasets  methods   base

 other attached packages:
 [1] rj_0.5.2-1

 loaded via a namespace (and not attached):
 [1] rJava_0.9-1  tools_2.13.1

 >   set.seed(123)
 >   print(coef(lm(dist~speed, data=cars)),digits=22)

               (Intercept)                    speed
 -17.57909489051087703615   3.93240875912408460735