R help - Sep 2009 - snowfall: missing MPI node

Hello,
I don't know if the question pertains to Rmpi, snow or snowfall.

I run my job by:

    mpirun -np N -hostfile $PBS_NODEFILE RMPISNOW -f my-script.r --slave

In the snowfall sfInit call I have to specify one less CPU respect to 
the mpirun call

    sfInit(parallel=TRUE, cpus=N-1, type="MPI")

otherwise I receive an error similar to: "cluster size N-1 already 
running" (sorry I don't remember the exact message)

Is this normal? In this case, if I want to call my script with - --cpus 
option I have to resort to inelegant shell scripting to obtain N-1 from 
the -mp argument.
In any case, is it possible to know in the script the number of 
processes (-np #) requested to mpirun?

Thanks for your time!
                                              mario

-- 
Ing. Mario Valle
Data Analysis and Visualization Group            | http://www.cscs.ch/~mvalle
Swiss National Supercomputing Centre (CSCS)      | Tel:  +41 (91) 610.82.60
v. Cantonale Galleria 2, 6928 Manno, Switzerland | Fax:  +41 (91) 610.82.82