give free growth as a flow, while —dfK, or —AdfK,, give the flow of thrift. Define the “productivity index” or “free growth index” @ (phi)as r/g or Ar/Ag, and the “thrift index” @ (theta) as -f /g or —Af /Ag.(A9.2) can then be put as g+@=1, (A9.2a) in either the continuous time or discrete period se