how to set the probabilty by useing neighbors variables

Hi all,
I want to use the neighbors variables which was wrote by Vagabon in Probabilistic Broadcast Agent class. I want to set the probability in the Agent/MessagePassing/MyPBCast instproc init function according to the number of neighbors, for instance if the number of neighbors equal 10 set prob_ 0.5 ,else set prob_ 1.

I do not know how could I use the neighbors variable in this class.
#Probabilistic Broadcast Agent
#V.B., 2005

Class Agent/MessagePassing/MyPBCast -superclass { Agent/MessagePassing }

Agent/MessagePassing/MyPBCast instproc init {} {
$self instvar prob_
$self instvar seqno_
$self instvar flag_
$self next
set seqno_ 0
set flag_ 0
$self instvar agent_addr_
set prob_ 1
$self set_pkttype 13
$self set packetSize_ 256
}

Agent/MessagePassing/MyPBCast instproc setprob {prob} {
$self instvar prob_
set prob_ $prob
}

Agent/MessagePassing/MyPBCast instproc setseed {seed} {
$self instvar seed_
set seed_ $seed
expr srand($seed_)
}

Agent/MessagePassing/MyPBCast instproc send {} {
$self instvar seqno_
$self instvar agent_addr_
set msg “pbcast:$agent_addr_:$agent_addr_:$seqno_:”
set flag_ 1
$self sendto 256 $msg -1 90
}

Agent/MessagePassing/MyPBCast instproc recv { flg port len p } {
# receiver function
$self instvar agent_addr_
$self instvar flag_
$self instvar prob_
set L [split $p :]
set src_ [lindex $L 2]
set seqno_ [lindex $L 3]
if {$flag_ == 1} { return }
set flag_ 1
#here toss a coin and make probabilistic decision
set coin [expr rand()]
#puts $coin
#puts $prob_
if {$coin > $prob_} { return }
set msg “pbcast:$agent_addr_:$src_:$seqno_:”
$self sendto 256 $msg -1 90

}
thanks