Chain programming over difference constraints

  • Authors:
  • K. Subramani;John Argentieri

  • Affiliations:
  • Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV;Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, WV

  • Venue:
  • Nordic Journal of Computing
  • Year:
  • 2006

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Abstract

Chain Programming is a restricted form of Linear Programming with a number of interesting properties. A Chain Program is characterized by a total ordering on the program variables (of a linear program). In other words, the constraints x1 ≤ x2...xn are either implicitly or explicitly part of the constraint system defined by a linear program. At the present juncture, it is not clear whether an arbitrary linear program augmented with a chain is easier to solve than linear programs in general, either asymptotically or computationally; however, it is definitely the case that Chain Programs possess a number of useful properties. In this paper, we restrict ourselves to linear programs that are constituted entirely of difference constraints. For such linear programs (also called Difference Constraint Systems), we show that the total ordering of the program variables results in an elegant divide and conquer algorithm for the problem of feasibility testing. This approach can be parallelized in straightforward fashion to run on any SIMD or MIMD architecture, thereby greatly enhancing its effectiveness. Inasmuch as difference constraint logic is an integral part of a number of verification problems in both Model-checking and real-time scheduling, our result is of particular importance to these communities. Secondly, difference constraint systems are duals of shortest path problems in directed graphs and hence our study is important from the perspectives of the Artificial Intelligence and Operations Research communities as well. One of the surprising consequences of our research is the establishment of a link between Chain Programs over Difference Constraints (CPD) and a specialized class of Totally Unimodular (TUM) matrices called interval matrices. This connection makes it likely that there exists a more efficient algorithm for the problem of feasibility testing in CPDs.