A forward model is a learned approximation of the physical environment
and it is used in series with an inverse model to form a composite
learning system. This learning system is capable of solving
the inverse mapping for non-convex regions of the solution
space,[, ]. The training technique for the
composite model is called distal learning and it is illustrated
in Figure . The learner controls a distal outcome via
a set of proximal variables which are inputs to a physical
environment, in our case a physical model of two violin strings. The
variable names and their functions for the composite system are
outlined in Table
.\
Table: Simulation Input and Output Variables