Examples walkthrough

SEM offers some examples in the form of python scripts in the examples/ folder. This page walks through these scripts, explains what they achieve and how they leverage the facilities provided by SEM with different objectives.

wifi_example.py

The full script is available here. This document will only show the relevant portions of the code.

This example showcases how SEM’s integration with the xarray python library can be leveraged to quickly obtain plots.

After running simulations through the sem.CampaignManager.run_missing_simulations() method, results are exported to an xarray data structure through the sem.CampaignManager.get_results_as_xarray() function:

##################################
# Exporting and plotting results #
##################################

# We need to define a function to parse the results. This function will
# then be passed to the get_results_as_xarray function, that will call it
# on every result it needs to export.
def get_average_throughput(result):
    stdout = result['output']['stdout']
    m = re.match('.*throughput: [-+]?([0-9]*\.?[0-9]+).*', stdout,
                  re.DOTALL).group(1)
    return float(m)

# Reduce multiple runs to a single value (or tuple)
results = campaign.get_results_as_xarray(params,
                                          get_average_throughput,
                                          'AvgThroughput', runs)

# We can then visualize the object that is returned by the function
print(results)

This function essentially goes over the specified parameter space, and applies a user-defined function to each one, to obtain some metrics. In the case of the wifi_example.py example, a get_average_throughput function is defined. This function takes as parameter a result, in the form of a dictionary with the following structure:

result = {
  'meta': {
    'id': Simulation ID,
    'elapsed_time': Time spent running the simulation,
  },
  'params': {
    'param1': Value,
    ...
  }
  'output': {
    'stdout': String containing output of simulation,
    'stderr': String containing errors of simulation,
    'filename': Contents of filename output file,
    ...
  }
}

and outputs a single value, which is obtained by parsing the stdout field of the output value. The resulting structure is then saved in the results variable, and can be inspected by using the print function.