Pascal Brisset

Solving the Kirkman's schoolgirl problem in a few seconds

In this paper, we propose an effective search procedure that interleaves two steps: subproblem generation and subproblem solution. We mainly focus on the first part. It consists of a variable domain value ranking based on reduced costs. Exploiting the ranking, we generate, in a Limited Discrepancy Search tree, the most promising subproblems first. An interesting result is that reduced costs provide a very precise ranking that allows to almost always find the optimal solution in the first generated subproblem, even if its dimension is significantly smaller than that of the original problem. Concerning the proof of optimality, we exploit a way to increase the lower bound for subproblems at higher discrepancies. We show experimental results on the TSP and its time constrained variant to show the effectiveness of the proposed approach, but the technique could be generalized for other problems.The Social Golfer Problem has been extensively used by the constraint community in recent years as an example of a highly symmetric problem. It is an excellent problem for benchmarking symmetry breaking mechanisms such as SBDS or SBDD and for demonstrating the importance of the choice of the right model for one problem. We address in this paper a specific instance of the Golfer Problem well known as Kirkmans Schoolgirl Problem and list a collection of techniques and tricks to find efficiently all its unique solutions. In particular, we propose SBDD+, a generic improvement over SBDD which allows a deep pruning when a symmetry is detected during the search. Our implementation of the presented techniques improves previously published results by an order of magnitude for CPU time as well as for number of backtracks. It computes the seven unique solutions of Kirkmans problem in a few seconds.

Graph Coloring for Air Traffic Flow Management

The aim of Air Traffic Flow Management (ATFM) is to enhance the capacity of the airspace while satisfying Air Traffic Control constraints and airlines requests to optimize their operating costs. This paper presents a design of a new route network that tries to optimize these criteria. The basic idea is to consider direct routes only and vertically separate intersecting ones by allocating distinct flight levels, thus leading to a graph coloring problem. This problem is solved using constraint programming after having found large cliques with a greedy algorithm. These cliques are used to post global constraints and guide the search strategy. With an implementation using FaCiLe, our Functional Constraint Library, optimality is achieved for all instances except the largest one, while the corresponding number of flight levels could fit in the current airspace structure. This graph coloring technique has also been tested on various benchmarks, featuring good results on real-life instances, which systematically appear to contain large cliques.

The Small Unmanned Meteorological Observer SUMO: A new tool for atmospheric boundary layer research

The Small Unmanned Meteorological Observer SUMO has been developed as a cost-efficient measurement system with the aim to close the existing observational gap of atmospheric measurement systems in between meteorological masts/towers and radiosondes. The system is highly flexible and has the capability for insitu ABL measurements with unique spatial and temporal resolution. SUMO is based on a light-weighted styrofoam model airplane, equipped with an autopilot system for autonomous flight missions and in its recent version with meteorological sensors for temperature, humidity and pressure. With its wingspan of 80 cm, its length of 75 cm and a total lift-off weight of 580 g, SUMO is easy to transport and operate even in remote areas with limited infrastructure. During several field campaigns in 2007 and 2008 the system has been successfully tested and operated. Atmospheric profiles of temperature, humidity, wind speed and wind direction have been determined up to 3500 m above ground during the FLOHOF (FLOw over and around HOFsjokull) field campaign in Central Iceland in July/August 2007. During a 3 week campaign on and around Spitsbergen in February/March 2008 the SUMO system also proved its functionality under polar conditions, reaching altitudes above 1500 m even at ground temperatures of -20°C and wind speeds up to 15 m s -1 .

Solving the Kirkman's Schoolgirl Problem in a Few Seconds

The Social Golfer Problem has been extensively used by the constraint community in recent years as an example of a highly symmetric problem. It is an excellent problem for benchmarking symmetry breaking mechanisms such as SBDS or SBDD and for demonstrating the importance of the choice of the right model for one problem. We address in this paper a specific instance of the Golfer Problem well known as Kirkman’s Schoolgirl Problem and list a collection of techniques and tricks to find efficiently all its unique solutions. In particular, we propose SBDD+, a generic improvement over SBDD which allows a deep pruning when a symmetry is detected during the search. Our implementation of the presented techniques improves previously published results by an order of magnitude for CPU time as well as for number of backtracks. It computes the seven unique solutions of Kirkman’s problem in a few seconds.

A ‘No-Flow-Sensor’ Wind Estimation Algorithm for Unmanned Aerial Systems:

A ‘no-flow-sensor’ wind estimation algorithm for Unmanned Aerial Systems (UAS) is presented. It is based on ground speed and flight path azimuth information from the autopilots GPS system. The algorithm has been tested with the help of the simulation option in the Paparazzi autopilot software using artificial wind profiles. The retrieval accuracy of the predefined profiles by the wind algorithm and its sensitivity to vertical aircraft velocity, diameter of the helical flight pattern and different data sampling methods have been investigated. The algorithm with a correspondingly optimized set of parameters is then applied to various scientific flight missions under real wind conditions performed by the UAS SUMO (Small Unmanned Meteorological Observer). The SUMO wind profiles are compared to measurements of conventional atmospheric profiling systems as radiosondes and piloted balloons. In general, the presented ‘no-flow-sensor’ wind estimation method performs well in most atmospheric situations and is now operationally used in the post-processing routine for wind profile determination from SUMO measurements.

Planning cordless business communication systems

The Popular tool uses constraint-based programming to optimize the placement of base stations for local wireless communication.

Placing base stations in wireless indoor communication networks

More and more mobile communications comes to company sites through local (typically indoor) wireless communication networks. However, planning wireless networks is quite different from planning traditional wire-based networks. Planning must take into account the specifics of radiowave propagation at the installation site. Current systems are cellular in that a base station (i.e. a sender or transmitter) controls the links to the transceivers. Buildings require multicellular systems because walls and floors absorb part of the radio signal. Today, an experienced salesperson estimates the number and positioning of base stations. To help the salesperson, Siemens has compiled a set of guidelines based on typical scenarios. However, a scenario might not always apply, and the approach does not handle positioning the base stations well. Computer-aided planning can help ease the difficulties of planning. Toward that end, we have developed Popular (Planning Of PicocellULAr Radio). The Popular prototype lets users compute the minimal number of base stations and their location, given a blueprint of the installation site and information about the wall and ceiling materials.

Optimal Placement of Base Stations in Wireless Indoor Telecommunication

Planning of local wireless communication networks is about installing base stations (small radio transmitters) to provide wireless devices with strong enough signals. POPULAR is an advanced industrial prototype that allows to compute the minimal number of base stations and their location given a blue-print of the installation site and information about the materials used for walls and ceilings. It does so by simulating the propagation of radio-waves using ray tracing and by subsequent optimization of the number of base stations needed to cover the whole building. Taking advantage of state-of-the-art techniques for programmable application-oriented constraint solving, POPULAR is among thefirst practical tools that can optimally plan wireless communication networks

SUMO: A small unmanned meteorological observer for atmospheric boundary layer research

A new system for atmospheric measurements in the lower troposphere has been developed and successfully tested. The presented Small Unmanned Meteorological Observer (SUMO) is based on a light-weighted commercially available model airplane, equipped with an autopilot and meteorological sensors for temperature, humidity and pressure. During the 5 week field campaign FLOHOF (Flow over and around HofsjoUkull) in Central Iceland the system has been successfully tested in July/August 2007. Atmospheric profiles of temperature, humidity, wind speed and wind direction have been determined up to 3500 m above ground. In addition the applicability of SUMO for horizontal surveys up to 4 km away from the launch site has been approved. During a 3 week campaign on and around Spitsbergen in February/March 2008 the SUMO system also proved its functionality under harsh polar conditions, reaching altitudes above 1500 m at ground temperatures of -20 °C and wind speeds up to 15 m s-1. With its wingspan of 80 cm, its length of 75 cm and its weight of below 600 g, SUMO is easy to transport and operate even in remote areas. The direct material costs for one SUMO unit, including airplane, autopilot and sensors are below 1200 Euro. Assuming at least several tenths of flights for each airframe, SUMO provides a cost-efficient measurement system with a large potential to close the existing observational gap of reasonable atmospheric measurement systems in between meteorological masts/towers and radiosondes.

A pragmatic reconstruction of Lambda-Prolog

Lambda-Prolog is a logic programming language in which hereditary Harrop formulas generalize Horn formulas, and simply typed lambda-terms generalize Prolog terms. One may wonder if these extensions are simultaneously required, and if useful subsets of lambda-Prolog can be defined, at least for pedagogical purposes. We answer this question by exhibiting a network of necessity links between the new features of lambda-Prolog. The starting point of the network is the demand for programming by structural induction on lambda-terms, and the necessity links give a rationale for such a programming style.