The above implementation strategy permits real-time simulation of the
general D-NURBS model on midrange graphics workstations. Lengthy
curves can be simulated at interactive rates, as can quadratic and
cubic surfaces on the order of 
control points. It is
possible to make simplifications that further reduce the computational
expense of (29) and
(31), making it practical to work with larger
D-NURBS surfaces.
First, it is seldom necessary to simulate the fully general D-NURBS
model throughout an entire sculpting session. Once we freeze the
values of the weights 
, all of the matrices in
(17) and (22) are constant
and their entries need no longer be recomputed at each time step.
With this restricted rational generalization of the B-splines,
interactive rates are readily obtained for much larger surfaces with
up to an order of magnitude more degrees of freedom. Note that
D-NURBS reduce to dynamic B-splines if all components of the frozen
vector are, in addition, equal to 1.
Second, a full implementation of (17) is
appropriate if the models must respond with realistic dynamics.
However, in certain CAGD and surface-fitting applications where the
modeler is interested only in the final equilibrium configuration of
the model, it makes sense to simplify (17) by
setting the mass density function 
to zero, so that the
inertial terms vanish. This economizes on storage and makes the
algorithm more efficient. With zero mass density,
(17) reduces to
while (22) reduces to
Discretizing the derivatives of 
and 
in
(32) and (33) with
backward differences, we obtain the integration formulas
and
respectively.
