## Version 1.0.2

To solve a sparse symmetric indeﬁnite system of linear equations. Given a sparse symmetric matrix $A={\left\{{a}_{ij}\right\}}_{n×n}$ and an $n$-vector $b$, this subroutine solves the system $Ax=b$.
The method used is a direct method using an ${LDL}^{T}$ factorization, where $L$ is unit lower triangular and $D$ is block diagonal with blocks of order 1 and 2. Advantage is taken of the extra sparsity available with $2×2$ pivots (blocks of $D$) with one or both diagonal entries of value zero. The numerical values of the entries are taken in account during the ﬁrst choice of pivots.