[Rcpp-devel] RNGScope

[Douglas Bates]

I think you want to move the RNGScope declaration before the calls to
rcauchy and runif.

On Tue, Aug 14, 2012 at 9:17 AM, Rodney Sparapani <rsparapa at mcw.edu> wrote:
> This is my first post so please be gentle ;o)  I have been through
> all of the docs that I can find (but I haven't looked at the source
> code directly).  Here is the behavior that I see:
>
>> require(inline)
> Loading required package: inline
>> source("helper.R")
>> source("corrMH.R")
>>
>> set.seed(66)
>>
>> for(i in 1:3) print(corrMH(0.2, 0.5, 100, 0))
> [1] -0.07071726
> [1] -8.085111
> [1] -4.004675
>>
>> corrMH.Rcpp <- cxxfunction(
> +  signature(a="numeric", b="numeric", N="numeric", x="numeric"),
> +  body=cat.file("corrMH.Rcpp.cpp"), plugin="Rcpp")
>>
>> set.seed(66)
>>
>> for(i in 1:3) print(corrMH.Rcpp(0.2, 0.5, 100, 0))
> [1] -0.07071726
> [1] -0.07071726
> [1] -0.07071726
>
> Notice that the Rcpp version of the function returns the same value
> each time (only 3 shown, but this is true no matter how many times
> that you do it).  I guess this is because we follow the RNGScope state
> of the RNG, but we don't update it.  However, updating is really needed
> in this case.  I hope I am making this clear.  Please let me know if
> you have any ideas.  Thanks
>
> Attachments seem to be allowed so I'm including my code...
>
> Red Hat Enterprise Linux Server release 6.2 (Santiago)
> g++ (GCC) 4.4.6 20110731 (Red Hat 4.4.6-3)
> R version 2.14.2 (2012-02-29)
>
>> installed.packages()["Rcpp", ]
>                      Package                      LibPath
>                       "Rcpp" "/opt/local/lib64/R/library"
>                      Version                     Priority
>                     "0.9.10"                           NA
>                      Depends                      Imports
>     "R (>= 2.12.0), methods"                           NA
>                    LinkingTo                     Suggests
>                           NA  "RUnit, inline, rbenchmark"
>                     Enhances                      OS_type
>                           NA                           NA
>                      License                        Built
>                 "GPL (>= 2)"                     "2.14.2"
> --
> Rodney Sparapani, PhD  Center for Patient Care and Outcomes Research
> Sr. Biostatistician               http://www.mcw.edu/pcor
> 4 wheels good, 2 wheels better!   Medical College of Wisconsin (MCW)
> WWLD?:  What Would Lombardi Do?   Milwaukee, WI, USA
>
> _______________________________________________
> Rcpp-devel mailing list
> Rcpp-devel at lists.r-forge.r-project.org
> https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel