Direct and approximate algorithmic methods for solving self-adjoint elliptic PDEs in three-space dimensions

The numerical implementation of the extended to the limit sparse LDL^T factorization solution methods for three-dimensional self-adjoint elliptic partial differential equations [3] is given. Two FORTRAN routines for the approximate (or exact) factorization of the coefficient matrix and solution of the resulting finite difference equations are supplied. The amount of fill-in terms can be controlled by the user through parameters R1, R2 the limiting case being when the matrix is factorized exactly.