  The subject of this paper is multigrid solvers for Helmholtz operators with
large wave numbers. Algorithms presented here are variations of the wave-ray
solver which is modified to allow efficient solutions for operators with
constant, continuous, and discontinuous wave numbers. Both geometric and
algebraic frameworks are employed, all yielding efficient and scalable solvers
at very little additional costs, compared to standard multigrid techniques. The
algorithms are implemented in one dimension, but with a clear extension to
higher dimensions.
