Loads a model description (its parameters) from a file.
Usage: load(file_name [,
attribute])
where file_name is the name of the file from which the description
is loaded; and attribute is an optional parameter, which allows
users to load only one specific parameter. It may be {pi, A,
B, all}, if the parameter that is to be loaded is pi, A, B,
or all of the previous, respectively.
Warning: When loading only specific parameters, like A, make sure
that the file from which it will be loaded has only that parameter stored in it,
and is in the format specified at the end of this section.