Blurb::
Basis function order of the model discrepancy

Description::

The order of the polynomial for the model discrepancy may be specified using 
the \c basis_order command, followed by either 0, for which a constant 
polynomial will be used, 1, for which a linear polynomial will be used, or 2, 
for which a quadratic polynomial will be used.

<b> Default Behavior </b>

By default, a quadratic polynomial is used.
