Signal class Feature Map

We need to define which of the nfeat feature sets are available to each signal class. When this mapping is not defined, it will be assumed that each signal class has access to all features. The variable class_feat_map is a cell array of length equal to the number of signal classes, for example:

   class_feat_map={ [1:6], [4 5 6], [1:2] };

The entries are the feature indexes (first index into funct_str - See Section 14.4.2). When undecided, use class_feat_map=[]; (empty), and the software will assume all features are available to each signal class.