Data Perturbation

The menu item Tools>Cross validation>data Perturbation can help escaping from local minima of the network's structure in which the network may be trapped. The network needs a database and the validation mode must be activated.

The BayesiaLab's structural learning algorithms are based on heuristic search. Therefore, they may be trapped into local minima. As the algorithms are using different heuristics, the local minima are not necessarily the same for all algorithms. Applying every algorithms and choosing the one with the lowest score is the first way to optimize the model. Data perturbation tool provides another solution consisting in adding noise to the weights associated with each line of the database in order to try escaping from local minima.

A noise is generated by using a Gaussian law, with 0 mean and the standard deviation set by the user. The selected learning algorithm is applied on this perturbed database and the score of the final structure is computed by using the original weights. The decay factor is applied after each iteration to reduce the standard deviation.

Parameters

Simply select the learning algorithm we want to use, and indicate the initial standard deviation, the decay factor and the number of tests to perform in the following dialog box:

An output directory can be specified where all networks learnt will be saved.

Depending on the chosen learning algorithm, a dialog box displays specific settings :

Analysis Report

Once the networks have been learnt, the following report is displayed :

This report is similar to the Arc Confidence except for the last table where the column indicating the Structure's Mean Score has been added.

The report can be saved in a HTML format file. It can also be printed. Two other options exist: displaying graphs and extracting the network.

Graphs

The Graphs button from the report allows displaying the graphical structure comparator. With this tool, data contained in reports can be viewed and interpreted easily.

Extracting the Network

The Network extraction button from the report displays network extraction tool. This tool allows building a network from any structure depending on arcs frequency thresholds.