INTERFACE SimpleSpring;

IMPORT Energy;

TYPE
  T <: Public;
  Public = Energy.T OBJECT
    length : REAL;                (* The referencial length of edge *)
    METHODS
      init(): T;
    END;
  (*
    The "spring" energy is computing assuming that every edge is a one
    elasticity wire that to pull or to push the extremal vertices with
    tension that depend of discrepancy between the "current" length of
    edge and their "referencial" or "nominal" length.
  *)
  
END SimpleSpring.