How to Deal with Unconventional Applications of Constraint Programming Charlotte Truchet TASC, LINA (UMR 6241), Université de Nantes, France Doctoral Program CP 2015 August 31st, 2015 Truchet Unconventional Applications CP2015-DP 1 / 46
Outline Conventional? Unconventional? 1 Two examples of unconventional applications 2 Urban Planning Music Lessons learned 3 Conclusion 4 Truchet Unconventional Applications CP2015-DP 2 / 46
Conventional? Unconventional? Classical application area Constraint Programming is a very powerful technology. Truchet Unconventional Applications CP2015-DP 3 / 46
Conventional? Unconventional? Classical application area Constraint Programming is a very powerful technology. BUT in practice, it is very often applied to a relatively small number of problems: scheduling, scheduling, scheduling, scheluding with something making it more difficult, scheduling with something else making it more difficult, etc Truchet Unconventional Applications CP2015-DP 3 / 46
Conventional? Unconventional? Classical application area See last year CP application tracks: Truchet Unconventional Applications CP2015-DP 4 / 46
Conventional? Unconventional? Classical application area Why? Maybe because it is difficult, in the NP-hard way ? Maybe because CP is indeed efficient on these problems? Maybe it is only cultural? Is there something wrong with this? Of course no. CP is used for what it’s good at. Does it say it all? No! (my claim) Truchet Unconventional Applications CP2015-DP 5 / 46
Conventional? Unconventional? What is CP good at? solving NP-hard problems, providing generic constraints (efficient, re-usable solving algorithms), providing generic constraint languages. Maybe, we focus a little too much on the first item, and not enough on the last two. Truchet Unconventional Applications CP2015-DP 6 / 46
Conventional? Unconventional? Unconventional applications? Conventional applications Scheduling, or any other application: naturally modeled by a CSP (no dirty variables or weird constraints), and which is NP-hard, and where the goal is to improve the solving time or the best optimum found so far. Truchet Unconventional Applications CP2015-DP 7 / 46
Conventional? Unconventional? Unconventional applications? Unconventional applications problems which are hard, or impossible, to model, or problems which may not be hard to solve considering the solving time, but hard to solve for other reasons, or problems which may even not need to be properly solved. NB there have already been a lot of such applications, for instance in medicine, computer aided design, image processing, oenology, disaster management... NB2 Actually, an unconventional application (drawing scenes with shadows) is at the origin of CP . See J.-F. Puget’s blog on CP history. Truchet Unconventional Applications CP2015-DP 7 / 46
Two examples of unconventional applications Outline Conventional? Unconventional? 1 Two examples of unconventional applications 2 Urban Planning Music Lessons learned 3 Conclusion 4 Truchet Unconventional Applications CP2015-DP 8 / 46
Two examples of unconventional applications Warnings and credits The application to music is an extract of my PhD thesis, defended at IRCAM (Institute for Research and Coordination Acoustics / Musique, Paris) in 2004. The work is a collaboration with my PhD advisors, G. Assayag and P . Codognet, and several researchers and musicians from IRCAM. The application to urban planning is a collaboration with Bruno Belin (Université de Nantes, France), Marc Christie (IRISA, France) and Frédéric Benhamou (Université de Nantes, France), between 2011 and 2014. Truchet Unconventional Applications CP2015-DP 9 / 46
Two examples of unconventional applications Warnings and credits In theses frames are real slides from past presentations (only a few of them): CPAIOR2014 for urban planning, JFPLC 2004 for music. In blue, I tell you how things really happened. Truchet Unconventional Applications CP2015-DP 9 / 46
Two examples of unconventional applications Urban Planning Evolution of the world city population [United Nations reports] 1995 the urban population in emerging countries is higher than the urban population of industrial countries, 2008 more than 50% of the world population lived in cities, 1/3 in townships, 2025 58% of the world population lives in cities (projection) 2050 67.2% of the world population lives in cities (projection) ⇒ Huge needs for the development of new cities, mostly in Africa = and Asia. The truth: thanks to Marc, we had a meeting with urban plan- ners he knew. They had problems which seemed interesting, highly combinatorial, and hard. Truchet Unconventional Applications CP2015-DP 10 / 46
Two examples of unconventional applications Urban Planning The SUSTAINS project a national-funded French research project, the project gathers urban planners and computer scientists Areva TA, Armines, Artelys, Artefacto, EPAMarne, LINA, LIMSI, goal : deploy a software suite for designing new cities, taking into account sustainability issues (energetic, social and economic), end-users are urban planners and decision makers. Early stage of urban planning: start with a beetroot field, draw a rough map for the decision makers and the population, used to have first estimations of the needs in big equipments. It is often easier to get money when working on such applica- tions, because: industrial, and original. Truchet Unconventional Applications CP2015-DP 11 / 46
Two examples of unconventional applications Urban Planning Existing urban models: UrbanSim [Waddell 2002], a land-use model, CommunityViz, a fine grain model for urban planners. We are not interested in fine grain information, pricing issues or time evolution of the future city. We use an ad-hoc urban model proposed by EPAMarne, which need very little information and does not model time evolution. A two stage approach: first step: a urban model calibrates the type of land use of the future city (EPAMarne), second step: a geographical constraint model computes the best possible map of the city. We started in the blind and had to read a totally new bibliogra- phy. But think about it: I’ve read scientific papers on SimCity. For work! Truchet Unconventional Applications CP2015-DP 12 / 46
Two examples of unconventional applications Urban Planning What is given: geographic data: area, rivers, landscape, existing elements (highways, historic places...), blocks: a 80m × 80m square, atomic element of the city, urban shapes: type of land use and buildings within a single block, macroscopic informations: intensities, centralities, economic indicators (number of inhabitants, employment rate, public services...). We spent hours of discussion, on almost two years, to under- stand these urban notions. We never fully understood, but we had reasonable assumptions to start with. Truchet Unconventional Applications CP2015-DP 13 / 46
Two examples of unconventional applications Urban Planning The constraint model is a permutation optimization problem: given data grid representation of the city, geographical informations, variables cells of the grid, domains urban shapes provided by the urban model, We never had a CSP . We explained to the urban planners what we could do, we made several prototypes (choosing the vari- ables and constraints ourselves), we improved them based on their remarks, and the CSP/model arrived in the end. Truchet Unconventional Applications CP2015-DP 14 / 46
Two examples of unconventional applications Urban Planning Core constraints: Interaction A cell of a given urban shape has location preferences and neighboorhood preferences. Example: shool units are attracted to residential units, and residential units are repelled by industrial units. Industrial units are attracted to rivers and roads. Preferences coefficients: one for each urban shape vs each type of landscape, and one for each urban shape vs each other urban shape. In discussions with the urban planners, the word "attraction" was often used. So we tried this as our first prototype and it happened to fit the urban planners view. Truchet Unconventional Applications CP2015-DP 15 / 46
Two examples of unconventional applications Urban Planning Higher level constraints Distance Some urban shapes must be placed with a minimum distance, expressed as a number of cells, between them. Example: between an individual house and a high building (R+7), there must be a minimum distance of 4 cells Critical size Some urban shapes must be grouped to have at minimum size (bigger than one cell). Example: highschools must be on at least two blocks. Areas with indus- trial activity must be big enough, otherwise, the area will not be created in practice because it will not be cost-effective. Once the base model was implemented, we showed some re- sults to the urban planners. At once, they saw situations that could not happen, and we refined the model from their obser- vations. Truchet Unconventional Applications CP2015-DP 16 / 46
Two examples of unconventional applications Urban Planning We got scared when we saw the size ot real-life problems (here, the french city of Marne-la-Vallée that we used as a test- case). Truchet Unconventional Applications CP2015-DP 17 / 46
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