if runway > goal {
		trigger = minTrigger
	} else {
		trigger = goal - runway
	}
	trigger = max(trigger, minTrigger)
	trigger = min(trigger, maxTrigger)
	if trigger > goal {
		print("trigger=", trigger, " heapGoal=", goal, "\n")
		print("minTrigger=", minTrigger, " maxTrigger=", maxTrigger, "\n")
		throw("produced a trigger greater than the heap goal")
	}
	return trigger, goal
}