fix sample means example

cluster

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+Subproject commit d556690348d9667689247704c8a2ddc20e35e632

demos/sample_means/cluster-master.665+1.734.log

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+	Host: cluster-master 	Rank(ID): 1 	of Size: 2 on comm 1 

demos/sample_means/cluster-master.666+1.717.log

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+	Host: cluster-master 	Rank(ID): 1 	of Size: 2 on comm 1 

demos/sample_means/cluster-master.669+1.714.log

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+	Host: cluster-master 	Rank(ID): 1 	of Size: 2 on comm 1 

demos/sample_means/cluster-master.888+1.898.log

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+	Host: cluster-master 	Rank(ID): 1 	of Size: 2 on comm 1 

demos/sample_means/generate_plots.R

@@ -1,11 +1,26 @@
-arg = commandArgs(TRUE)
+if ( !is.loaded("mpi_initialize") ){
+	library(Rmpi)
+}
 
-samples = rep(NA, 100000)
-for ( i in 1:100000 ){ samples[i] = mean(rexp(40, 0.2)) }
+number_of_plots = 5
+nodes = mpi.universe.size()
+mpi.spawn.Rslaves(nslaves=nodes)
 
-jpeg(paste('plots/', arg, '.jpg', sep=""))
+generate_plot <- function(filename){
+	samples = rep(NA, 100000)
+	for ( i in 1:100000 ){ samples[i] = mean(rexp(40, 0.2)) }
+	
+	jpeg(paste('plots/', filename, '.jpg', sep=""))
+	
+	hist(samples, main="", prob=T)
+	lines(density(samples), col="darkblue", lwd=3)
+	
+	dev.off()
+}
 
-hist(samples, main="", prob=T)
-lines(density(samples), col="darkblue", lwd=3)
+samples = 1:number_of_plots
 
-dev.off()
+mpi.apply(samples, generate_plot)
+
+mpi.close.Rslaves()
+mpi.quit()