  Given a differential equation with infinite-dimensional symmetry pseudo-group
it is shown, using an example, that it is generally not possible to construct
enough joint invariants to form an invariant numerical scheme of the equation.
To circumvent this problem, we propose to discretize the symmetry pseudo-group
action. Using the theory of moving frames, joint invariants of the discretized
action are algorithmically constructed. Computer simulations indicate that
numerical schemes constructed from these joint invariants can produce better
numerical results than standard schemes.
