Sir...in this script，i understand whole script but not getting what
set-cx
set-cy
set-cz..

DBR script
.......................................
set opt(chan) Channel/UnderwaterChannel
set opt(prop) Propagation/UnderwaterPropagation
set opt(netif) Phy/UnderwaterPhy
set opt(mac) Mac/UnderwaterMac/BroadcastMac
set opt(ifq) Queue/DropTail/PriQueue
set opt(ll) LL
set opt(energy) EnergyModel
set opt(txpower) 2.0
set opt(rxpower) 0.75
set opt(initialenergy) 10000
set opt(idlepower) 0.008
set opt(ant) Antenna/OmniAntenna
set opt(filters) GradientFilter ;# options can be one or more of
;# TPP/OPP/Gear/Rmst/SourceRoute/Log/TagFilter
set opt(minspeed) 0 ;#minimum speed of node
set opt(maxspeed) 3 ;#maximum speed of node
set opt(speed) 0.5 ;#speed of node
set opt(position_update_interval) 0.3 ;# the length of period to update node's position
set opt(packet_size) 50 ;#50 bytes
set opt(routing_control_packet_size) 20 ;#bytes

set opt(ifqlen) 50 ;# max queue length in if
set opt(nn) 6 ;# number of nodes
set opt(x) 1000 ;# X dimension of the topography
set opt(y) 10 ;# Y dimension of the topography
set opt(z) 10
set opt(seed) 11
set opt(stop) 500 ;# simulation time
set opt(prestop) 90 ;# time to prepare to stop
set opt(tr) "a.tr" ;# trace file
set opt(datafile) "a.data"
set opt(nam) "a.nam" ;# nam file
set opt(adhocRouting) DBR
set opt(interval) 10.0
set opt(range) 100 ;#range of each node in meters

if { $argc > 0 } {
set opt(seed) [lindex $argv 0]
set opt(nn) [lindex $argv 1]
set opt(datafile) [lindex $argv 2]
}

puts "the file name is $opt(datafile)"
puts "the sending interval is $opt(interval)"

# ==================================================================

LL set mindelay_ 50us
LL set delay_ 25us
LL set bandwidth_ 0 ;# not used

Queue/DropTail/PriQueue set Prefer_Routing_Protocols 1

# unity gain, omni-directional antennas
# set up the antennas to be centered in the node and 1.5 meters above it
Antenna/OmniAntenna set X_ 0
Antenna/OmniAntenna set Y_ 0
#Antenna/OmniAntenna set Z_ 1.5
Antenna/OmniAntenna set Z_ 0.05
Antenna/OmniAntenna set Gt_ 1.0
Antenna/OmniAntenna set Gr_ 1.0

Mac/UnderwaterMac set bit_rate_ 1.0e4 ;#10kbps
Mac/UnderwaterMac set encoding_efficiency_ 1
Mac/UnderwaterMac/BroadcastMac set packetheader_size_ 0 ;# #of bytes

# Initialize the SharedMedia interface with parameters to make
# it work like the 914MHz Lucent WaveLAN DSSS radio interface
Phy/UnderwaterPhy set CPThresh_ 10 ;#10.0
Phy/UnderwaterPhy set CSThresh_ 0 ;#1.559e-11
Phy/UnderwaterPhy set RXThresh_ 0 ;#3.652e-10
#Phy/WirelessPhy set Rb_ 2*1e6
Phy/UnderwaterPhy set Pt_ 0.2818
Phy/UnderwaterPhy set freq_ 25 ;# 25khz
Phy/UnderwaterPhy set K_ 2.0 ;# spherical spreading

# =================================================================
# Main Program
# =================================================================

#
# Initialize Global Variables
#
#set sink_ 1
set ns_ [new Simulator]
set topo [new Topography]

$topo load_cubicgrid $opt(x) $opt(y) $opt(z)
$ns_ use-newtrace
set tracefd [open $opt(tr) w]
$ns_ trace-all $tracefd

set nf [open $opt(nam) w]
$ns_ namtrace-all-wireless $nf $opt(x) $opt(y)


set data [open $opt(datafile) a]


set total_number [expr $opt(nn)-1]
set god_ [create-god $opt(nn)]


$ns_ at 0.0 "$god_ set_filename $opt(datafile)"


set chan_1_ [new $opt(chan)]


global defaultRNG
$defaultRNG seed $opt(seed)


$ns_ node-config -adhocRouting $opt(adhocRouting) \
-llType $opt(ll) \
-macType $opt(mac) \
-ifqType $opt(ifq) \
-ifqLen $opt(ifqlen) \
-antType $opt(ant) \
-propType $opt(prop) \
-phyType $opt(netif) \
#-channelType $opt(chan) \
-agentTrace OFF \
-routerTrace OFF \
-macTrace ON\
-topoInstance $topo\
-energyModel $opt(energy)\
-txPower $opt(txpower)\
-rxPower $opt(rxpower)\
-initialEnergy $opt(initialenergy)\
-idlePower $opt(idlepower)\
-channel $chan_1_


#Set the Sink node


set node_(0) [ $ns_ node 0]
$node_(0) set sinkStatus_ 1
$god_ new_node $node_(0)
$node_(0) set X_ 500
$node_(0) set Y_ 0
$node_(0) set Z_ 0
$node_(0) set passive 1

set rt [$node_(0) set ragent_]
$rt set control_packet_size $opt(routing_control_packet_size)

set a_(0) [new Agent/UWSink]
$ns_ attach-agent $node_(0) $a_(0)
$a_(0) cmd set-range $opt(range)
$a_(0) cmd set-target-x -20
$a_(0) cmd set-target-y -10
$a_(0) cmd set-target-z -20
$a_(0) cmd set-filename $opt(datafile)
$a_(0) cmd set-packetsize $opt(packet_size) ;# # of bytes



set node_(1) [ $ns_ node 1]
$node_(1) set sinkStatus_ 1
$god_ new_node $node_(1)
$node_(1) set X_ 440
$node_(1) set Y_ 0
$node_(1) set Z_ 0
$node_(1) set passive 1

set rt [$node_(1) set ragent_]
$rt set control_packet_size $opt(routing_control_packet_size)
$node_(1) set max_speed $opt(maxspeed)
$node_(1) set min_speed $opt(minspeed)
$node_(1) set position_update_interval_ $opt(position_update_interval)
set a_(1) [new Agent/UWSink]
$ns_ attach-agent $node_(1) $a_(1)
$a_(1) cmd set-range $opt(range)
$a_(1) cmd set-target-x -20
$a_(1) cmd set-target-y -10
$a_(1) cmd set-target-z -20
$a_(1) cmd set-filename $opt(datafile)
$a_(1) cmd set-packetsize $opt(packet_size) ;# # of bytes
#$node_(1) move

set node_(2) [ $ns_ node 2]
$node_(2) set sinkStatus_ 1
$node_(2) random-motion 1
$node_(2) set max_speed $opt(maxspeed)
$node_(2) set min_speed $opt(minspeed)
$node_(2) set position_update_interval_ $opt(position_update_interval)

$god_ new_node $node_(2)
$node_(2) set X_ 380
$node_(2) set Y_ 0
$node_(2) set Z_ 0
$node_(2) set passive 1

set rt [$node_(2) set ragent_]
$rt set control_packet_size $opt(routing_control_packet_size)

set a_(2) [new Agent/UWSink]
$ns_ attach-agent $node_(2) $a_(2)
$a_(2) cmd set-range $opt(range)
$a_(2) cmd set-target-x -20
$a_(2) cmd set-target-y -10
$a_(2) cmd set-target-z -20
$a_(2) cmd set-filename $opt(datafile)
$a_(2) cmd set-packetsize $opt(packet_size) ;# # of bytes
#$node_(2) move


set node_(3) [ $ns_ node 3]
$node_(3) set sinkStatus_ 1
$node_(3) random-motion 1

$node_(3) set max_speed $opt(maxspeed)
$node_(3) set min_speed $opt(minspeed)
$node_(3) set position_update_interval_ $opt(position_update_interval)

$god_ new_node $node_(3)
$node_(3) set X_ 320
$node_(3) set Y_ 0
$node_(3) set Z_ 0
$node_(3) set passive 1

set rt [$node_(3) set ragent_]
$rt set control_packet_size $opt(routing_control_packet_size)

set a_(3) [new Agent/UWSink]
$ns_ attach-agent $node_(3) $a_(3)
$a_(3) cmd set-range $opt(range)
$a_(3) cmd set-target-x -20
$a_(3) cmd set-target-y -10
$a_(3) cmd set-target-z -20
$a_(3) cmd set-filename $opt(datafile)
$a_(3) cmd set-packetsize $opt(packet_size) ;# # of bytes




set node_(4) [ $ns_ node 4]
$node_(4) set sinkStatus_ 1
$node_(4) random-motion 1

$node_(4) set max_speed $opt(maxspeed)
$node_(4) set min_speed $opt(minspeed)
$node_(4) set position_update_interval_ $opt(position_update_interval)

$god_ new_node $node_(4)
$node_(4) set X_ 260
$node_(4) set Y_ 0
$node_(4) set Z_ 0
$node_(4) set passive 1

set rt [$node_(4) set ragent_]
$rt set control_packet_size $opt(routing_control_packet_size)

set a_(4) [new Agent/UWSink]
$ns_ attach-agent $node_(4) $a_(4)
$a_(4) cmd set-range $opt(range)
$a_(4) cmd set-target-x -20
$a_(4) cmd set-target-y -10
$a_(4) cmd set-target-z -20
$a_(4) cmd set-filename $opt(datafile)
$a_(4) cmd set-packetsize $opt(packet_size) ;# # of bytes




#Set the source node
set node_($total_number) [$ns_ node $total_number]
$god_ new_node $node_($total_number)

$node_($total_number) set sinkStatus_ 1

$node_($total_number) set X_ 200
$node_($total_number) set Y_ 0
$node_($total_number) set Z_ 0
$node_($total_number) set-cx 200
$node_($total_number) set-cy 0
$node_($total_number) set-cz 0
set rt [$node_($total_number) set ragent_]
$rt set control_packet_size $opt(routing_control_packet_size)


set a_($total_number) [new Agent/UWSink]
$ns_ attach-agent $node_($total_number) $a_($total_number)
$a_($total_number) cmd set-range $opt(range)
$a_($total_number) cmd set-target-x 500
$a_($total_number) cmd set-target-y 0
$a_($total_number) cmd set-target-z 0
$a_($total_number) cmd set-filename $opt(datafile)
$a_($total_number) cmd set-packetsize $opt(packet_size) ;# # of bytes
$a_($total_number) set data_rate_ [expr 1.0/$opt(interval)]

# make nam workable
set node_size 10
for {set k 0} { $k<$opt(nn)} {incr k} {
$ns_ initial_node_pos $node_($k) $node_size
}


set opt(stop2) [expr $opt(stop)+200]


puts "Node $total_number is sending first!!"
$ns_ at 1.33 "$a_($total_number) cbr-start"
$ns_ at $opt(stop).001 "$a_($total_number) terminate"

$ns_ at $opt(stop2).002 "$a_(0) terminate"


$ns_ at $opt(stop2).003 "$god_ compute_energy"
$ns_ at $opt(stop2).004 "$ns_ nam-end-wireless $opt(stop)"
$ns_ at $opt(stop2).005 "puts "NS EXISTING..."; $ns_ halt"


puts $data "New simulation...."
puts $data "nodes = $opt(nn), maxspeed = $opt(maxspeed), minspeed = $opt(minspeed), random_seed = $opt(seed), sending_interval_=$opt(interval))"
puts $data "x= $opt(x) y= $opt(y) z= $opt(z)"
close $data
puts "starting Simulation..."
$ns_ run

Please use CODE tags when posting blocks of code. If you understand the whole script...seems odd you don't understand those three lines. How did you write that code without understanding what you're doing??? If you are wanting visual output, wouldn't that require and X, Y, and Z boundary/coordinate? Since they are cx, cy, and cz....that's what they are/do. Have you run this code, and tried experimenting with different values?