Using pvmloop

	- 'pvmloop' is a PVM program I wrote to facilitate running batches of
	processes over a pvm.

	- see ~kaiser/imcat/pvmloop.html and 'man pvmloop' for more info

	- it doesn't do anything you couldn't do with rsh and shell script
	but is more convenient and more efficient

	- pvmloop works with 'pvmserver' and 'topvm' programs

	- basic usage: 

		pvmloop n_iterations command_template

	1) it starts a number of pvmserver processes on the nodes of the pvm 
	2) it sends them command strings generated from the command_template
	3) pvmservers execute commands with system() command and arranges
	for stdout and stderr from child processes to be sent back to the
	master pvmloop process.
	4) it kills the pvmserver processes when finished

	- pvmloop needs a 'pvmslaves.lst' file to tell it 'nnodes' and which nodes to use
	and associate a string with each server (typically used to identify scratch
	disks).  e.g.
		3
		01	node01
		02	node02
		03	node03

	- commands generated from command_template by sustituting:
		%i	iteration number 		e.g. 0,1,2,...11
		%I	formatted iteration number	e.g. 00, 01, 02, .... 11
		%n 	node number 
		%N	node string
		%%	%

	- examples
		pvmloop 3 'df -k /d%N'			# check scratch disk space
		pvmloop 3 '/usr/ucb/ps -aux | head -5'	# check on cpu use
		pvmloop 12 'rm /d%N/kaiser/tmp/image.%I.fits'	# delete some images

	- allows simulation of cluster on single machine (duplicates in pvmslaves.lst)

	- works in 'round robin' fashion - sends out batches of nnodes commands

	- no load balancing

	- no killing of spawned child processes on abnormal exit