[R] Need help using Rcpp + Rmpi

Dirk Eddelbuettel edd at debian.org
Tue Jun 25 00:12:41 CEST 2013

Hi Mollyy,

On 24 June 2013 at 14:53, Molly Davies wrote:
| Hello,
| This might belong in the R-devel category, but I am not a C / C++
| programmer, so I thought I'd start here. I have just written my first R

The convention is that package-specific question go to the package specific
forums. In this case, you should really subscribe to rcpp-devel and post there.

| extension using Rcpp, and it is SO much faster than my best R efforts,
| thank you for such a wonderful package!

On behalf of the team: You are very welcome.

| Instead of writing a separate text | file, I used the following:
| ### begin R ###
| require(Rcpp)
| cppFunction('
| double s2nICm(NumericVector ICvec, int m, double In, double sampleSize) {
|   int n = ICvec.size();
|   double covSum = 0.0;
|   double s2n = 0.0;
|   double ss = sampleSize*sampleSize;
|   for(int i=0; i<=m-1; i++){
|     for(int k=0; k<=i+m; k++){
|       covSum += ICvec[i]*ICvec[k];
|     }
|   }
|   for(int i=m; i<=n-m-1; i++){
|     for(int k=i-m; k<=i+m; k++){
|       covSum += ICvec[i]*ICvec[k];
|     }
|   }
|   for(int i=n-m; i<=n; i++){
|     for(int k=i-m; k<=n; k++){
|       covSum += ICvec[i]*ICvec[k];
|     }
|   }
|   s2n = (In/ss) * covSum;
|   return s2n;
| }
| ')
| ### end R ###
| This works perfectly on my laptop (Macbook air). Now I need to use this
| function as a part of a large simulation on my school's cluster (running
| Sun Grid Engine) using Rmpi. I included the above function in a text file,
| sourced that file in the master and sent the function above to my slaves
| using
| mpi.bcast.Robj2slave(s2nICm)
| I've been trying to get this to work for about a week now, but no luck.
| (The original Rmpi simulation code that included the old, slow R version of
| the function above worked without error). Until recently, I've been getting
| a steady stream of informative error messages that I've forwarded to our
| sys admin - problems with g++, etc. Now I'm not getting any error messages,
| I'm just not getting any results. There may still be a problem with our
| cluster, but I'm wondering if perhaps I'm doing something wrong, too. I'd
| really like to understand how Rcpp and Rmpi interact. Is it OK to call
| cppFunction('...') in the master and then send the resulting R function to
| slaves using mpi.bcast.Robj2slave()? Or do I need to send a text version of
| the cppFunction('...') to each slave and evaluate the text within each
| slave? What's the proper way to use Rcpp within the context of Rmpi? Does
| anyone know of any good resources out there that can help me understand
| what's going on under the hood?

In a nutshell, you need the Rcpp-using code on each node -- that means object
code and all the object code needs. But let's discuss on rcpp-devel.

Cheers, Dirk

| Thanks very much for your time,
| Molly Davies
| Biostatistics Graduate Student
| UC Berkeley
| 	[[alternative HTML version deleted]]
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Dirk Eddelbuettel | edd at debian.org | http://dirk.eddelbuettel.com

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