[R-SIG-Mac] Snow package on bi-proc G5

[Simon Urbanek]

Naji,

On Jun 15, 2005, at 12:36 PM, Naji wrote:

> I'm running complex simulations and I'd like to distribute half the  
> simulation on each processor (one G5 machine)
> The R code looks like
>
> For (rep in 1:replications) # 300 replications
> {
> # the simulations results are stored in an array
> Is it possible to distribute the simulations on both proc..?

Yes.

I use pvm as back-end for snow, but I guess others should work, too.  
Example (very simple and stupid but should illustrate the idea):

 > library(snow)
Loading required package: rpvm
 > cl<-makeCluster(2)  # use 2 CPUs
 > clusterApplyLB(cl,1:6,function(x) mean(x+rnorm(10)))
[[1]]
[1] 0.836866

[[2]]
[1] 1.755120

[[3]]
[1] 3.385007

[[4]]
[1] 3.751311

[[5]]
[1] 4.805047

[[6]]
[1] 5.89379

When running simulations you may want to set the seed differently for  
each process [something like clusterApply(cl, 1:2, set.seed)] or use  
one of the RNG libraries, otherwise both CPUs will give you the same  
results - probably not what you want ;).

Cheers,
Simon