[Rd] Randomness not due to seed

[Duncan Murdoch]

On 11-07-19 8:01 PM, Mike Marchywka wrote:
>
>
>
>
>
>
>
> ----------------------------------------
>> Date: Tue, 19 Jul 2011 06:13:01 -0700
>> From: jeroen.ooms at stat.ucla.edu
>> To: r-devel at r-project.org
>> Subject: [Rd] Randomness not due to seed
>>
>> I am working on a reproducible computing platform for which I would like to
>> be able to _exactly_ reproduce an R object. However, I am experiencing
>> unexpected randomness in some calculations. I have a hard time finding out
>> exactly how it occurs. The code below illustrates the issue.
>>
>> mylm1<- lm(dist~speed, data=cars);
>> mylm2<- lm(dist~speed, data=cars);
>> identical(mylm1, mylm2); #TRUE
>>
>> makelm<- function(){
>> return(lm(dist~speed, data=cars));
>> }
>>
>> mylm1<- makelm();
>> mylm2<- makelm();
>> identical(mylm1, mylm2); #FALSE
>>
>> When inspecting both objects there seem to be some rounding differences.
>> Setting a seed does not make a difference. Is there any way I can remove
>> this randomness and exactly reproduce the object every time?
>
> I don't know if anyone had a specific answer for this

I think Bill Dunlap's answer addressed it:  the claim appears to be false.

Duncan Murdoch

but in general floating point is not
> something for which you want to make bitwise equality tests. You can check the Intel
> website for some references but IIRC the FPU can start your calculation with bits or
> settings ( flushing denorms to zero for example) left over from the last user although I can't document that.
>
> for example, you can probably find more like this suggesting that changes in alignmnet
> and rounding in preamble code can be significant,
>
> http://software.intel.com/en-us/articles/consistency-of-floating-point-results-using-the-intel-compiler/
>
> and of course if your algorithm is numerically sensitive results could change a lot. Now
> its also possible you have unitiliazed or corrupt memory, but you would need to
> consider that you will not get bit wise reproduvibility. You can of course go to java
> if you really want that LOL.
>
>
>>
>>
>>
>>
>>
>> --
>> View this message in context: http://r.789695.n4.nabble.com/Randomness-not-due-to-seed-tp3678082p3678082.html
>> Sent from the R devel mailing list archive at Nabble.com.
>>
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>   		 	   		
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel