Atom-Specific RDF Descriptors

By restricting RDF descriptors to certain atom types an atom-specific RDF descriptor. 

The resulting descriptor is simpler than a complete one and is useful if the ignored atom type has no meaning for the task to be represented — for instance, by ignoring hydrogen atoms with t = H (ignore mode). 

The opposite approach is a descriptor that is calculated in exclusive mode for a certain atom type with the inverse condition 

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