Solving the Salinity Control Problem in a Potable Water System

Abstract. Salinity is the relative concentration of salts in water. In a city of southern China, the local water supply company pumps water from a nearby river for potable use. During the winter dry season, the intrusion of sea water raises the salinity of the river to a high level and affects approximately the daily life of 450,000 residents of the city. This paper reports the application of constraint programming (CP) to optimize the logistical operations of the raw water system so as to satisfy the daily water consumption requirement of the city and to keep the potable salinity below a desirable level for as many days as possible. CP is the key to the success of the project for its separation of concerns and powerful constraint language that allows for rapid construction of a functional prototype and production system. Flexibility and adaptiveness allow us to deal with our clients' many changes in the requirements. Deriving good variable and value ordering heuristics, and generating useful implied constraints, we demonstrate that branch-and-bound search with constraint propagation can cope with an optimization problem of large size and great difficulty

Removing propagation redundant constraints in redundant modeling

A widely adopted approach to solving constraint satisfaction problems combines systematic tree search with various degrees of constraint propagation for pruning the search space. One common technique to improve the execution efficiency is to add redundant constraints, which are constraints logically implied by others in the problem model. However, some redundant constraints are propagation redundant and hence do not contribute additional propagation information to the constraint solver. Redundant constraints arise naturally in the process of redundant modeling where two models of the same problem are connected and combined through channeling constraints. In this paper, we give general theorems for proving propagation redundancy of one constraint with respect to channeling constraints and constraints in the other model. We illustrate, on problems from CSPli