title: NS2 nam does not show anythings
body: <p>I have created a <code>tcl</code> file that works fine but when I execute <code>nam out.nam</code> the nam app does not show any things, Can any one help me? </p>
  
  <pre><code># Some constants
  set area_width      100
  set area_height     100
  set stop_time       20
  
  # MAC stuff
  Mac/802_11 set dataRate_    2.0e6
  Mac/802_11 set RTSThreshold_    3000
  
  # Define the simulator
  set simulator [new Simulator]
  
  set trace_file  [open out.tr w]
  
  $simulator trace-all $trace_file
  
  #Open the NAM trace file
  set nam_file [open out.nam w]
  $simulator namtrace-all $nam_file
  
  #Adjusting the topography
  set topography [new Topography]
  $topography load_flatgrid $area_width $area_height
  
  # General Operations Director
  create-god 2
  
  # Some configuration just as same as the expamle 'ex6sta.tcl'
  $simulator node-config -adhocRouting    DumbAgent \
                   -llType    LL \
                   -macType   Mac/802_11 \
                   -ifqType   Queue/DropTail/PriQueue \
                   -ifqLen    50 \
                   -antType   Antenna/OmniAntenna \
           -propType  Propagation/FreeSpace \
                   -phyType   Phy/WirelessPhy \
                   -channelType   Channel/WirelessChannel \
                   -topoInstance  $topography \
                   -agentTrace    ON \
                   -routerTrace   OFF \
                   -macTrace  OFF \
           -movementTrace OFF
  
  set host(1) [ $simulator node ]
  set host(2) [ $simulator node ]
  
  $host(1) set X_ 20
  $host(1) set Y_ 20
  $host(1) set Z_ 0.0
  
  $host(2) set X_ 70
  $host(2) set Y_ 70
  $host(2) set Z_ 0.0
  
  # Connection 1 UDP
  set udp [new Agent/UDP]
  $simulator attach-agent $host(1) $udp
  set sink [new Agent/Null]
  $simulator attach-agent $host(2) $sink
  $simulator connect $udp $sink
  set cbr [new Application/Traffic/CBR]
  $cbr set packetSize_ 1000
  $cbr set interval_ 0.005
  $cbr attach-agent $udp
  $simulator at 5.0  "$cbr start"
  
  # invoking finish procedure
  $simulator at $stop_time "finish"
  
  proc finish {} {
      global simulator host cbr nam_file trace_file
      $host(1) reset
      $host(2) reset  
      $cbr stop
      $simulator flush-trace
      close $nam_file 
      close $trace_file
      $simulator halt
      puts "Finished"
  }
  
  puts "Starting Simulation..."
  $simulator run
  </code></pre>
  
  <p>Note that I use <code>ns 2.34</code> on <code>ubuntu 12.4</code></p>