eLearning

methods of optimal control; these methods lead
naturally to shadow pricing rules (of the type
sketched above for oil) for every stock in the system.
At this level, the model is much the same as that
envisaged by ecologists to represent the natural
world, except that we incorporate stocks created by
the economic system (such as human and physical
capital), try to identify places where the economic
planner can influence the outcome (control vari-
ables), and seek to optimize.
At this point, we are very far away from the
capacity to construct such a model, much less
analyze it. Many elements of system interaction are
unknown, and the state of the art in computation
limits the number of stocks to a handful at best. The
challenge now is to construct meaningful models
that capture important components of interaction. I
hope and believe that ecologists’ experience in
modeling the natural world can be a valuable input
to this endeavor.