I'm a bit confused about Full Approximation Storage (FAS). My understanding is that based on the correction equations being solved, mutligrid methods categorized into Correction Scheme or FAS and can be done for both Algebraic and Geometric Multigrid methods. Is that correct. Also, what is the difference b/w Full Multigrid and FAS. thanks.

Full multigrid method, you start from the coarest grid, on the other hand V-cycle, starts from the finest grid. FAS could be applied by Full multigrid and V-cycle.