Algorithms

In this section we introduce a generic view of the algorithm class in PLASMA Lab. For this purpose we consider the case of a local (non distributed) algorithm. The implementation of distributed algorithms is presented in the next section.

InterfaceAlgorithmFactory

As presented before, algorithms factories implements the Plugin interface. They are responsible for parsing the algorithm’s parameters and constructing the scheduler class of the algorithm.

As each algorithm needs various parameter as input, we developed generic objects to declare these parameters. Each algorithm factory declares a list of SMCParameter objects. This list is then used by PLASMA Lab to retrieve correct values from the user.

First we present each type of parameters. Then we describe the way a list of parameter is used and values retrieved by PLASMA Lab.

SMCParameter

The SMCParameter class is the parent class of all parameters. Its basic attributes are a name, a tip and a Boolean that defines if the parameter represents a Boolean value or not.

Used alone, an SMCParameter represents a simple text, double or Boolean value.

SMCOption

A SMCOption is a Boolean parameter that contains a list of other SMCParameter. If the SMCOption is set to true, its children parameters are enabled and can be filled by the user.

SMCOption behaves like a check box object, and it is represented by one in PLASMA Lab GUI.

SMCAlternatives

An SMCAlternative is a Boolean parameter that contains a list of other SMCParameter and points to another SMCAlternative (like the linked list mechanism). If the SMCAlternative is set to true, its children parameters are enabled and can be filled, while every other SMCAlternative in the linked list are set to false.

An SMCAlternative behaves like a radio button object, and it is represented by one in PLASMA Lab GUI.

SMCObjectParameter

An SMCObjectParameter defines a parameter to be an AbstractModel. It is specifically used in the CUSUM algorithm, that needs to be executed on two different models (the basic GUI can only select one model).

The SMCObjectParameter is interpreted by the PLASMA Lab GUI as a ComboBox containing models from the currently selected project.

Parameters workflow

  • Creating parameter widgets

An InterfaceAlgorithmFactory object defines a list of SMCParameter that correspond to their algorithm. This list is accessed by the ParametersPanel class using the getParametersList method. A widget (CheckBox, RadioButton, TextField, ...) is created in the GUI for each parameter, including children parameters. Some widgets depend on their parent widget to be enabled.

  • Retrieving parameters values

When launching a new experiment, the ExperimentPanel access to the ParametersPanel corresponding to the selected algorithm and retrieves a map of String/Object pairs. For each pair, the String corresponds to the name of the parameter (as provided by the InterfaceAlgorithmFactory and displayed on the widget) and the Object is the value of the parameter. As said previously, the value could be of type Boolean, String, or even AbstractModel.

Additional parameters may be added to the map such as distributed, which informs the system if a distributed version of an algorithm should be used.

The map and the selected InterfaceAlgorithmFactory is then transmitted to the ExperimentationManager. The ExperimentationManager calls the createScheduler function on the factory with the parameters map as an argument. This function parses the values of the parameters and it checks if they suit the algorithm. It then creates an instance of the InterfaceAlgorithmScheduler ready to be executed and returns it.

  • Alternative workflows

The previous method to retrieve parameters values requires the use of widgets, which may be unavailable with user interfaces different than the GUI (command line, interface with another tool, ...).

An alternative workflow (used by the command line) is to construct directly a map of parameters name and values, defined by the user. In that case the user must be aware of which parameters and values are valid and necessary. The map is then transmitted to the createScheduler function.

Another solution is to call the fillParametersMap method of InterfaceAlgorithmFactory. This method converts an array of parameters values (written as String values) into a map of String/Object pairs. This method fills the map with the parameters value taken from the array by converting the values to their correct types. The content and the order of the parameters in the String array is however entirely dependant of the InterfaceAlgorithmFactory implementation.

InterfaceAlgorithmScheduler

public interface InterfaceAlgorithmScheduler extends Runnable

This class provides the main interface for an SMC algorithm (both local or distributed). This interface extends the Runnable interface. Thus an algorithm will have a run method.

public void setExpListener(ExperimentationListener listener);

The InterfaceAlgorithmScheduler also defines a setExpListener method. Object implementing the ExperimentationListener interface will be kept up to date on the experiment progress using calls to functions such as notifyAlgorithmStarted, notifyAlgorithmCompleted and publishResults.

public void abortScheduling();

The abortScheduling method is called when the user wants to stop a running experiment before it finishes.

Run method of an SMC Algorithm

The run method of an SMC Algorithm is where the work is done. For instance the run method of the basic Monte Carlo algorithm could be based on the following pseudo-code:

initialize(model, property)
listeners.notifyAlgorithmStarted

while(continue)
    state = model.newPath
    positive += property.check(state)
    total ++
    if(total > required)
        continue = false

listeners.publishResults(getResults(positive))
listeners.notifyAlgorithmCompleted

For each run, the model initializes a new trace. The property is checked starting from the initial state. If the property has been checked on enough traces, the algorithm terminates and the results are published.

AbstractAlgorithm

This class provides a generic implementation of the basic methods for an SMC algorithm. It provides in particular an initializeAlgorithm method that should be called at the beginning of the run method. This method initializes optimization attributes of the algorithm.

SMCResult

The data structure used to return results of an experimentation is the SMCResult interface. This interface inherits from ResultInterface.

In PLASMA Lab, a class implementing the ResultInterface represents the output of a task such as a simulation or an experiment. It provides access to a header array of type String with each header being associated to a value.

The SMCResult interface adds a specific getPr method to get a single result of the experiment. This result is a double value, that represents for instance a probability or a Boolean value with 1 meaning true and 0 meaning false. Other results are accessed by the getValue method of ResultInterface.