LDL is a set of concise routines for factorizing symmetric positive-definite sparse matrices, with some applicability to symmetric indefinite matrices. Its primary purpose is to illustrate much of the basic theory of sparse matrix algorithms in as concise a code as possible, including an elegant new method of sparse symmetric factorization that computes the factorization row-by-row but stores it column-by-column. This package is part of SuiteSparse. AMD is an optional dependency and will be used if found. It is primarily used for this package's test suite.