Common issues/gotchas

Below we list common issues and gotchas encountered when using SuperScreen, along with the recommended solutions. If you encounter an issue not listed here, or the recommended solution does not work for you, please open an issue on GitHub.

  • Device.make_mesh() hangs for a superscreen.Device with transport terminals.


    In order to correctly set the boundary conditions for films with transport terminals (see Terminal currents), SuperScreen generates a mesh for such films where the boundary vertices of the mesh are exactly the same as the boundary vertices of the associated superscreen.Polygon. As a result, Device.make_mesh() can hang if the distance between vertices in the film superscreen.Polygon is greater than the max_edge_length requested in Device.make_mesh(). To fix this, simply increase the number of points in the superscreen.Polygon defining the film. For example, to double the number of points in the polygon, run:

    polygon.points = polygon.resample(2 * len(polygon.points))
  • Poor performance when running SuperScreen in multiple Python processes.


    SuperScreen uses numba to automatically perform some computations in parallel across multiple CPUs. To avoid competition between multiple Python processes running SuperScreen, you can set the number of threads available to numba in each process. For example, if your computer has 8 physical CPU cores and you are running SuperScreen in 2 different Python processes, you should tell numba to use 8 / 2 = 4 threads in each Python process.

    import joblib
    import numba
    # Number of Python processes in which you will run SuperScreen
    number_of_python_processes = 2
    # Number of physical CPU cores available
    physical_cpus = joblib.cpu_count(only_physical_cores=True)
    # Tell numba how many threads to use in each Python process
    numba.set_num_threads(int(physical_cpus / number_of_python_processes))

    For more details, see Setting the Number of Threads in the numba documentation.

    A similar problem can occur when running SuperScreen on a cluster using a scheduler such as Slurm. numba sets the default number of threads according to multiprocessing.cpu_count(), which does not know about the number of CPUs requested from the scheduler. On the other hand joblib.cpu_count() does know about the number of CPUs allocated by the scheduler. Therefore, when running SuperScreen on such a cluster you should always run

    import joblib
    import numba

    or set the environment variable NUMBA_NUM_THREADS prior to importing numba/superscreen.