1. A graph processing system, comprising: a graph API (Application Program Interface), as executed on a processor of a computer and as capable of implementing any of a plurality of graph operators to express computations of input graph analytics applications; a run-time system, executed by the processor, to implement graph operators specified by each graph API function and to deploy the implemented graph operators to a selected computing system; and a library of multiple implementations for each graph API function, each implementation predetermined as being optimal for a specific set of conditions met by a graph being processed, for functional capabilities of a specific computing system on which the graph is being processed, and for resources available on that specific computing system.