Highlights

MultiGrid.
This Numerical Method is never going to work for
Hyperbolic Equations.
I have proved it for the 1D case. But 1D is embedded in 3D.
So the result is
valid for 3D as well.
Nevertheless, there is ongoing research on this topic,
in vain.

MultiGrid.
There exist only two flavours for grid refinement
and grid coarsening:
DoubleGrid and
TripleGrid.

The distinction between Continuous and Discrete is only gradual,
not essential:
 Least Squares Finite Element Method.
Can only be formulated properly as a
Unification of
Finite Elements and Finite Differences.
Two applications: Ideal Flow in
2D and
3D.
The concept of Dual Elements is important with L.S.FEM.

Unification of Finite Elements and Finite Differences for
Convection and Diffusion can be accomplished via
Resistor Networks
in 2D and 3D.