Constrained graph layout by stress majorization and gradient projection

The adoption of the stress-majorization Method from multi-dimensional scaling into graph layout has provided an improved mathematical basis and better convergence properties for so-called "force-directed placement" techniques. In this paper we explore algorithms for augmenting such stress-majorization techniques with simple linear constraints using gradient-projection optimization techniques. Our main focus is a particularly simple class of constraints called "orthogonal-ordering constraints" but we also discuss how gradient-projection methods may be extended to solve more general linear "separation constraints". In addition, we demonstrate several graph-drawing applications where these types of constraints can be very useful. (C) 2008 Elsevier B.V. All rights reserved.