Blurb::
Specify how the trial samples are generated
Description::
The user has the option to specify the method by which the 
trials are created to adjust the centroids. The \c trial_type
can be one of three types:
\li \c random, where points are generated randomly
\li \c halton, where points are generated according to the Halton sequence
\li \c grid, where points are placed on a regular grid over the hyperspace. 

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