Sign controlled solvers for the absolute value equation with an application to support vector machines

Abstract: Let $A$ be a real $n\times n$ matrix and $z,b\in \mathbb R^n$. The piecewise linear equation system $z-A\vert z\vert = b$ is called an absolute value equation. It is equivalent to the general linear complementarity problem, and thus NP hard in general. Concerning the latter problem, three solvers are presented: One direct, one semi-iterative and one discrete variant of damped Newton. Their previously proved ranges of correctness and convergence, respectively, are extended. Their performance is compared on instances of the XOR separation problem for support vector machines which can be reformulated as an absolute value equation.