R help - Mar 2007 - Snow Package and SPRNG: Will it solve my problem?

Hello and thanks in advance for your time.  I currently have a  
simulation running on my cluster with the help of snow that relies on  
global variables being changes regularly  to random values.  It uses  
these values, lets call them x1 x2 and x3, in custom functions for  
logliklyhood and score that gets used in the standard optim function.   
To get set in the global table on the different nodes I'm generating  
the random value in a function on the node and then using the  
superassign operator ( <<- ) to set it to the global variable.
(eg:
    temp = rand(n1)
    x1 <<- sort(temp)
)

) I'm worried that this is creating a lot of avoidable message  
passing.  Here are my questions:

Does the superassign operator set the global variable on the head  
node, like I believe it does, or rather does it only set it on the  
local global table?

Does the SPRNG package offer a viable replacement for useless message  
passing of random values like this?

Thanks again for your continued help with my problems.

On Wed, 21 Mar 2007, robert.robinson at maine.edu wrote:
> Hello and thanks in advance for your time.  I currently have a
> simulation running on my cluster with the help of snow that relies on
> global variables being changes regularly  to random values.  It uses
> these values, lets call them x1 x2 and x3, in custom functions for
> logliklyhood and score that gets used in the standard optim function.
> To get set in the global table on the different nodes I'm generating
> the random value in a function on the node and then using the
> superassign operator ( <<- ) to set it to the global variable.
> (eg:
>    temp = rand(n1)
>    x1 <<- sort(temp)
> )
>
> ) I'm worried that this is creating a lot of avoidable message
> passing.  Here are my questions:
>
> Does the superassign operator set the global variable on the head
> node, like I believe it does, or rather does it only set it on the
> local global table?
There is not shared global environments eath node has its own separate
from the master's.
>
> Does the SPRNG package offer a viable replacement for useless message
> passing of random values like this?
>
rsprng and rlecuyer (the current default) address a different issue --
ensuring (reproducible if necessary) independent streams on the nodes.

Best,

luke
> Thanks again for your continued help with my problems.
>
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-- 
Luke Tierney
Chair, Statistics and Actuarial Science
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa                  Phone:             319-335-3386
Department of Statistics and        Fax:               319-335-3017
    Actuarial Science
241 Schaeffer Hall                  email:      luke at stat.uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu