The package structure is in flux.

The skyline matrices are currently created from the "coordinate" representation of a sparse matrix.

using SkylineSolvers, DataDrop
K = DataDrop.retrieve_matrix("K.h5")
@show size(K)
I, J, V = findnz(K)     
sky = SkylineSolvers.Ldlt2.SkylineMatrix(I, J, V, size(K, 1))

The two main operations are "factorize" and "solve":

SkylineSolvers.Ldlt2.factorize!(sky)
b = rand(size(A, 1))
x = SkylineSolvers.Ldlt2.solve(sky, b)
@test norm(A \ b - x) / norm(x) < 1e-6

At the moment, after factorization sky holds the factorized matrix, but there are no functions to extract the individual factors.

• The package is divided into several modules.
• The package is intended for symmetric indefinite matrices (except the Cholesky decomposition requires a positive definite matrix).
• The modules define the type SkylineMatrix, which are mutually incompatible. In each module the matrix is stored under a skyline, and only one half of the matrix is actually stored.
• The module Chol defines a Cholesky decomposition and triangular solve.
• The modules Ldlt, Ldlt2, Ldlt3 define a LDLT decomposition and triangular solve each. All of these implementations are roughly equally fast.
• The module Ldlt3 is most pleasing aesthetically: the sparse solver looks almost identical to the dense-matrix solver.
• The module Colsol defines the original skyline solution from the textbook of KJ Bathe.
• No renumbering is undertaken in order to minimize the number of entries stored below the skyline. If the matrix is numbered in an unfortunate way, use the package SymRCM to reorder the matrix first.
• The solvers in this package are many times slower than the SuiteSparse Cholesky supernodal solver. However, they should be able to take as inputs arbitrary integers and floating point numbers.