Build a headless version of a NetLogo code

This page will guide you towards using your program with graphical widgets and NetLogo in OpenMOLE. For this combination to work, some rules have to be applied to your program.


  • Limit your usage of widget implicit globals. We prefer explicit globals using the globals primitive, because you need to re-define all the important values from your program in OpenMoLE before you launch it on a remote computing environment.
  • Do not use the same functions setup and go to setup your program on a remote environment. On the remote environment, the NetLogo program is initialised and launched only once, so there is no need to call a clear-all primitive with each setup. When running on distributed environments, clear-all is not your best friend. clear-all erases all the globals passed by OpenMoLE to your program before it starts and will make it crash.
  • Do not directly use the implicit globals created by means of a widget. Although you can you can access and overwrite implicit globals in OpenMole, it prevents OpenMoLE from mapping explicitly its Prototypes to the NetLogo globals.
  • NetLogo is a graphical framework. As such, many variables of a model developed in NetLogo are set through widgets (a graphical component). In the NetLogo World, setting or getting a value on the model inputs is generally achieved by calling set or get on the widget object. In OpenMoLE however, the NetLogo program has to be parameterised without the GUI. Models must be used in headless mode with OpenMole. This is not a problem because globals with unspecified values in the OpenMole NetLogo Task will take the default values defined in widgets.

    Still, having a lot of parameters defined in your model might make you forget to override values in OpenMOLE. As a result, NetLogo would take widget values and your model would run a thousand times with a wrong set of parameter values! Let's study a simple method to avoid such a situation. This approach invites you to define all the parameters of your models prior to any run of your NetLogo models in OpenMOLE.

    Application to the Fire model

    Fire.nlogo has a widget slider named density which is a global implicit.

    This excerpt shows the initial-trees and burned-trees variables which are explicit globals. They can be used directly in OpenMOLE.

    We propose here a simple method to better organise your code in order to make it manipulable by OpenMOLE:
    • First we do not use the implicit globals, so we create an explicit global variable, myDensity, corresponding to the implicit one (density) :
    • Second, we use this new variable in the setup procedure (it replaces the former):

      And we update the explicit variable with the former implicit density variable
      At this moment, your program does not work any more in NetLogo, it’s normal, don’t panic :).

    • Third, we call this function in our setup function, after the clear-all primitives.
    • Now, the program works in NetLogo’s graphical mode. We still need to create another setup function without the call to clear-all and to init-globals. Remember that these two calls don't cope well with distributed executions.
    • }

      The program is now ready to be parameterised and manipulated by OpenMOLE \o/

      Think you're ready for the next level? Check this other tutorial to learn how OpenMOLE can help you calibrate your NetLogo model using Genetic Algorithms.