A method for operating a powertrain system to transfer torque among an engine, torque machines, and a driveline includes identifying a speed/torque search window responsive to a parameter affecting engine power output and the output torque request. A search is executed to determine a preferred engine operating point for operating the powertrain system in response to an output torque request. The search includes determining a candidate power cost associated with operating the powertrain system at the candidate engine torque and candidate engine speed for each of a plurality of candidate engine speeds and candidate engine torques within the speed/torque search window. A preferred engine operating point is determined as the candidate engine speed and the candidate engine torque associated with a minimum of the candidate power costs. Engine operation is controlled responsive to the preferred engine speed.