ADAPT fragment descriptors

The adaptations introduced in the fast exchange algorithm to optimize the UCC criterion allow selection from databases of hundreds of thousands of compounds. Currently, the implementation is limited to tens of continuous descriptors, though discrete descriptors like fragment counts could be handled in principle. Further work is also needed for even larger databases with hundreds of descriptors. 

Recently, this fragment constant method has been implemented in a routine and interfaced to ADAPT (45,46). Thus, the estimated log P value for a molecule can be used as a descriptor along with all the other descriptor types. 

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