[R] Error in clusterApply(): recursive default argument reference

[nicolas bertin]

Hi,

I want to compute a distribution of the intersection of a graph and
'randomized' graphs induced by the permutations of node labels (to
preserve the graph topology).
Since I ll have many permutations to perform, I was thinking of using
the snow package and in particular "parSapply" to divide the work
between my 4 CPUs.
But I get the following error message :

Error in clusterApply(cl, splitList(x, length(cl)), lapply, fun, ...) : 
        recursive default argument reference

What am i doing wrong ?

Some details about my platform and R version :
-----------------------------------------------
$platform
[1] "x86_64-redhat-linux-gnu"
$version.string
[1] "R version 2.4.1 (2006-12-18)"


Below is the snippet of code generating the error message :
-----------------------------------------------------------
### libraries ###
library(graph)
library(snow)

### functions ###
nullDistribIntersection <- function(g1, g2, perm=1000)
{
  n1 <- nodes(g1)
  sapply(1:perm,
	  function(i)
	  {
            nodes(g1) <- sample(n1)
	    numEdges(intersection(g1,g2))
	  }
	 )
}


parNullDistribIntersection <- function(g1, g2, perm=1000, cl=cl)
{
  n1 <- nodes(g1)
  parSapply(cl, 1:perm,
	  function(i)
	  {
            nodes(g1) <- sample(n1)
	    numEdges(intersection(g1,g2))
	  }
	 )
}


## initialize the graph and the rand seed
set.seed(123)
g <- randomEGraph(LETTERS[1:15], edges = 100)

## compute a distribution of the intersection of the graph 
## and a 'randomized' graph induced by the permutations of
## node labels (to preserve the graph topology)
cat("1CPU sys time:",
    system.time(
                 dist <- nullDistribIntersection(g,g)
               ),
    "\n"
    )

cl <- makeCluster(c("localhost", "localhost"), type = "SOCK")
cat("Cluster sys time:",
    system.time(
                 dist <- parNullDistribIntersection(g,g)
               ),
    "\n"
    )
----------------------------------------------------------------

Thanks in advance.

Nicolas Bertin 
GSC / RIKEN Yokohama