Reordering algorithm for minimization of ram usage of a skyline matrix

The stiffness matrix of $Ax=B$ system of linear equations, where $A$ is an $n\times n$ symmetric matrix stored in the form of symmetric skyline matrix, that is associated with a finite element model of 3-D elastic solids, when reordered with the reverse Cuthill–McKee algorithm doesn't result in a skyline matrix with limited RAM storage space requirements as would happen with a 2-D problem.

What is the best algorithm for the 3-D case?

• What do you do with A? Solve by it? Directly or iteratively? Compute eigenmodes? – rchilton1980 Apr 30 '18 at 18:01
• I want to solve it directly and the stiffness matrix is very large even when renumbered with RCM algorithm. However for the same number of unknowns for a 2d problem the renumbered stiffness matrix requires (1/5) amount of ram. – Student Apr 30 '18 at 18:22