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Using the package Rmpi requires a sound scripting in order to distribute the work and handle the communication. In addition, a script is necessary the make the workers available to R at the beginning. This part is usually shipped with an .Rprofile, located either in the working or in the HOME directory.

There are multiple ways to ensure that:

• copy the .Rprofile into the working directory (e.g. cp ~/R/x86_64-unknown-linux-gnu-library/2.15/Rmpi/Rprofile ./.Rprofile)
• .Rprofile located in HOME
• set the environment variable R_PROFILE that points to any file holding the

required contents, this might be done within the jobfile, “.bashrc” or in a module file

Using the package doMPI enables parallization with foreach loops in R. See the package documentation for details.

In order to starts the jobs properly, there must not be a .Rprofile available within the current environment.

An example for doMPI and a corresponding job script.

start_par_R.sh

	#!/bin/bash
	# show commands being executed, per debug
	set -x
 
	# Set job parameters
	######################################################################
	## check what MPI implementation is loaded before setting the parameter
	## module list ??
	#BSUB -a openmpi
 
	# Set number of CPUs
	#BSUB -n 16
 
	# name of the output file
	#BSUB -o 16_cpus.out
 
 
	# Start R MPI job
	mpirun.lsf ./dompi_example.R

And the R-script that is called.

dompi_example.R

#!/usr/local/bin/Rscript
 
# that is the path to Rscript on the cluster, might be different on your local machine
 
################################################################################################
 
#       Filename: dompi_example.R
 
#       Author: Stefan Luedtke
 
#       Created: Saturday 18 August 2012 14:16:36 CEST
 
#       Last modified: Tuesday 04 March 2014 15:52:00 CET
 
################################################################################################
#       PURPOSE         ########################################################################
# 
# This script should illustrate the use of the "doMPI" package on the HP-Cluster of GFZ.
#
# Of course, a basic knowledge of R is required. 
#
# First, we will perform a hierarchical clustering algorithm of some random data. Second,
# a group validation indices will be computed for each level of the resulting tree.
# Although the first bit is done quite fast, the computation of the validation indices
# might take a long time. This will be done in parallel.
 
########################
 
# The "doMPI" package, together with the foreach package, is an easy to apply framework for
# parallel processing but must be handled with care. We will come back to this later- take
# care. 
 
########################
 
# Note: Since the word "cluster" might be used in two different contexts we define here,
# that: If we talk about the machine we use "hpcluster", when talking about the algorithms,
# validation and so on, we stick to the word "cluster".
 
################################################################################################
################################################################################################
 
	################################################################################################
	################################################################################################
 
	################################################################################################
 
	rm(list=ls())
 
	################################################################################################
	library(reshape)	# general stuff
 
	library(cluster)	# used for the cluster algorithms
	library(fpc)		# used for the cluster validation
 
	library(doMPI)		# framework for the Rmpi package
	library(foreach)	# parallel backend 
 
	################################################################################################
 
 
	# create some random data in a matrix, make them reproducible 
 
	set.seed(1)
	data=matrix(c(runif(300, min=100, max=1000), rnorm(300, mean=-100, sd=2)), ncol=2)
 
 
	# create distance matrix the cluster algorithm requires
	dist_mat=dist(data, method="euclidean")
 
 
	#compute the cluster Dendrogramm for the data
	cluster_fit=hclust(dist_mat, method="ward")
 
	#	!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!	#
	#	!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!	#
	#	!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!	#
	#	!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!	#
 
	# 	That bit runs distributed over multiple nodes specified in the
	# 	jobscript compute cluster validation indices for each cluster 
	#	class, we only check classes 2 to nrow(data)/2
 
	cl = startMPIcluster()	# we do not give a number here, which means we take as much as we
				# get- managed by the startup script
 
	registerDoMPI(cl) 	# register cl for the foreach framework
 
 
	cluster_groups=foreach(i=c(2:(nrow(data)/2)), .combine=cbind, 
				  .packages=c("cluster","fpc"))%dopar%
	{
		cluster.stats(dist_mat, cutree(cluster_fit, k=i), G2=T)
	}
 
	closeCluster(cl)
 
	#	!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!	#
	#	!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!	#
	#	!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!	#
	#	!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!	#
 
	#extract indices of interest, that is a list of names as returned by the function
	# "cluster.stat", see the help for more information
 
	indices=c("cluster.number", "dunn", "dunn2", "g2")
 
	cluster_performance=as.data.frame(t(cluster_groups[which(row.names(cluster_groups) 
				%in% indices==TRUE),]))
 
	row.names(cluster_performance)=NULL
 
 
	## save the R workspace as ".Rdata" in the working dir (optional of course)
	save.image()
	###############################################################################################
	################################################################################################

doMPI provides a simple framework that allows running parallel applications almost no extra effort. However, this does not make sense at all time. Is the single iteration pretty fast, a serial implementation makes more sense because the communication overhead will slow down the entire process.

A more flexible framework is provided by the Rmpi implementation, which is not as easy the implement. A popular example can be found at at this page.