An introduction to Choco

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1 An introduction to Choco A java Constraint Programming Library G. Rochart, N. Jussien, X. Lorca Charles Prud'homme, Hadrien Cambazard, Guillaume Richaud, Julien Menana, Arnaud Malapert Bouygues SA, École des Mines de Nantes (LINA CNRS UMR 6241) '08/05 OSSICP'08 Choco 1 / 25

2 The Choco constraint solver Outline 1 The Choco constraint solver A little bit of history The design of Choco General features 2 The practice of Choco 3 Choco around the World 4 The future of Choco 5 Acknowledgements '08/05 OSSICP'08 Choco 2 / 25

3 The Choco constraint solver A little bit of history A solver for teaching and research 1999 : a rst CLAIRE implementation within the OCRE project an national initiative for an open constraint solver for both teaching and research (Nantes, Montpellier, Toulouse, Bouygues, ONERA) 2003 : a rst Java implementation portability, ease of use for newcomers, etc : Choco V2 a clear separation between the model and the solving machinery ; a complete re-factoring ; a user-oriented version '08/05 OSSICP'08 Choco 3 / 25

4 The Choco constraint solver A little bit of history An open constraint solver An open system a source forge project BSD license for all possible usages A glass box designed for both teaching and research ecient yet readable readable yet ecient '08/05 OSSICP'08 Choco 4 / 25

5 The Choco constraint solver The design of Choco General Schema of Choco's Architecture Model (1) generic model of a constraint (2) generic model of a variable (3) API for creating variables and constraints How to make a problem? CP-Model implementation of a Model in the CP paradigm Choco Solver API Solver (1) constraints data structures (2) variables data structures (3) data structures related to the search algorithm CP-Solver (1) data structure implementation (2) parser from CP-Model to CP-Solver How to solve a problem? Memory (1) trailing (2) recomputation (3) copying '08/05 OSSICP'08 Choco 5 / 25

6 The Choco constraint solver General features Embedded Variable Types A wide variety of variable paradigms : Integer variables : enumerated and bounded, Set variables : enumerated and bounded, Real variables, Composite variables : integer expression and real expression composed with operators like plus, mult, minus, scalar, sum, power,... (rst-class citizen) Work in progress : Intervals list. '08/05 OSSICP'08 Choco 6 / 25

7 The Choco constraint solver General features A Large Choice of Implemented Constraints About 70 available constraints in Choco : Classical arithmetic constraints : equal, not equal, less or equal, greater or equal, A large set of useful global constraints : AllDierent and BoundAllDierent, GlobalCardinality and BoundGCC, AtMostNvalue, Cumulative, Occurence, Element,... Exclusive constraints : Tree,... Reied constraints : and, or, not, implies, ifonlyif,... '08/05 OSSICP'08 Choco 7 / 25

8 The Choco constraint solver Search-related tools General features User can use predened search methods : Searching CSP solutions : solve for searching rst solution and solveall for searching all solutions Optimizing a problem by maximizing ou minimizing a variable value (maximize and minimize) with or without restart Some new feature in next release like solve with restarts (useful for heuristics with learning)... '08/05 OSSICP'08 Choco 8 / 25

9 The Choco constraint solver Embedded Search Heuristics General features Choco proposes a set of implemented Search Heuristics. Two kinds are distinguished : Variable choice : MinDomain, RandomIntVarSelector, StaticVarOrder, DomOverDeg, DomOverDynDeg, DomOverWDeg, DomOverFailureDeg, LexIntVarSelector,... Value choice for a Variable : DecreasingDomain, IncreasingDomain, MaxVal, MinVal, MidVal, RealIncreasingDomain, RandomIntValSelector, RandomSetValSelector,... '08/05 OSSICP'08 Choco 9 / 25

10 The practice of Choco Outline 1 The Choco constraint solver 2 The practice of Choco A First Problem The Nqueens problem Custom branching Good Practice 3 Choco around the World 4 The future of Choco 5 Acknowledgements '08/05 OSSICP'08 Choco 10 / 25

11 The practice of Choco x + y = z A First Problem Two parts : the Model and a Solver. Model m = new CPModel() ; Solver s = new CPSolver() ; '08/05 OSSICP'08 Choco 11 / 25

12 The practice of Choco x + y = z A First Problem Two parts : the Model and a Solver. Model m = new CPModel() ; Solver s = new CPSolver() ; Model = Variables + Expressions + Constraints. IntegerVariable v1 = makeboundintvar(v1,1,5) ; IntegerVariable v2 = makeboundintvar(v2,1,5) ; IntegerVariable v3 = makeboundintvar(v3,1,5) ; IntegerExpressionVariable e1 = plus(v1,v2) ; Constraint c1 = eq(v3,e1) ; '08/05 OSSICP'08 Choco 11 / 25

13 The practice of Choco x + y = z A First Problem Two parts : the Model and a Solver. Model m = new CPModel() ; Solver s = new CPSolver() ; Model = Variables + Expressions + Constraints. IntegerVariable v1 = makeboundintvar(v1,1,5) ; IntegerVariable v2 = makeboundintvar(v2,1,5) ; IntegerVariable v3 = makeboundintvar(v3,1,5) ; IntegerExpressionVariable e1 = plus(v1,v2) ; Constraint c1 = eq(v3,e1) ; Linking Variables and Constraints m.addvariable(v1,v2,v3) ; m.addconstraint(c1) ; '08/05 OSSICP'08 Choco 11 / 25

14 The practice of Choco x + y = z A First Problem Two parts : the Model and a Solver. Model m = new CPModel() ; Solver s = new CPSolver() ; Model = Variables + Expressions + Constraints. IntegerVariable v1 = makeboundintvar(v1,1,5) ; IntegerVariable v2 = makeboundintvar(v2,1,5) ; IntegerVariable v3 = makeboundintvar(v3,1,5) ; IntegerExpressionVariable e1 = plus(v1,v2) ; Constraint c1 = eq(v3,e1) ; Linking Variables and Constraints m.addvariable(v1,v2,v3) ; m.addconstraint(c1) ; Feeding the Model to the Solver s.read(m) ; s.solve() ; '08/05 OSSICP'08 Choco 11 / 25

15 The practice of Choco Problem and Variables declaration The Nqueens problem A well-known problem : the nqueens problem Model and Solver declarations Model m = new CPModel() ; Solver s = new CPSolver() ; A model using three kinds of Variables IntegerVariable[] q = new IntegerVariable[n] ; IntegerVariable[] d1 = new IntegerVariable[n] ; IntegerVariable[] d2 = new IntegerVariable[n] ; i [1, n], q[i] = makeenumintvar(q+i,1,n) ; i [1, 2 n], d1[i] = makeenumintvar(d1-+i,1,2 n) ; i [1, 2 n], d2[i] = makeenumintvar(d2-+i, n,n) ; '08/05 OSSICP'08 Choco 12 / 25

16 The practice of Choco Constraint declaration The Nqueens problem Model and Solver declarations A model using three kinds of Variables Equality (channeling) constraints are dened : Constraint[] equalities = new Constraint[2 n] ; int i,j = 0 ; while (i < n) { equalities[j] = eq(d1[i],plus(q[i],i)) ; equalities[j+1] = eq(d2[i],minus(q[i],i)) ; i++ ; j+=2 ; } AllDierent constraints are dened Constraint[] alldiff = new Constraint[3] ; alldiff[0] = alldifferent(q) ; alldiff[1] = alldifferent(d1) ; alldiff[2] = alldifferent(d2) ; '08/05 OSSICP'08 Choco 13 / 25

17 The practice of Choco The Nqueens problem Relating Variables and Constraints Model and Solver declarations A model using three kinds of Variables Constraint declaration. Relating Variables and Constraints in the Model. m.addvariable(q) ; m.addvariable(d1) ; m.addvariable(d2) ; m.addconstraint(equalities) ; m.addconstraint(alldiff) ; '08/05 OSSICP'08 Choco 14 / 25

18 The practice of Choco Search Heuristic and Resolution The Nqueens problem Model and Solver declarations A model using three kinds of Variables Constraint declaration. Relating Variables and Constraints in the Model. Feeding the Model to the Solver : s.read(m) ; A search heuristic : choosing a Variable whose domain has a minimum size... s.setvarintselector(new MinDomain(s,s.getVar(q))) ; Resolution begins... s.solve() ; '08/05 OSSICP'08 Choco 15 / 25

19 The practice of Choco Custom branching Customizing the search Customizing the search can be done by custom branching (for instance) Creating an AbstractargeIntBranching class s.attachgoal(new DichotomicBranching(s.getVar(q))) ;... DichotomicBranching extends AbstractLargeIntBranching { Implementing some functions like public int getfirstbranch(object x) { return 1 ; } public int getnextbranch(...) { return i+1 ; } public boolean finishedbranching(..) { return i == 2 ; } public void godownbranch(..)... {... int middle = (var.getsup() + var.getinf()) / 2 ; if (i == 1) var.setsup(middle) ; else var.setinf(middle + 1) ; '08/05 OSSICP'08 Choco 16 / 25

20 The practice of Choco In a few words Good Practice Keep your mind, in Choco : Modeling and search are separated through Model and Solver Variables and Constraints are separated from Model and Solver The Choco philosophy : an open, user-oriented constraint solver a clear separation between model and solver a living solver '08/05 OSSICP'08 Choco 17 / 25

21 Choco around the World Outline 1 The Choco constraint solver 2 The practice of Choco 3 Choco around the World 4 The future of Choco 5 Acknowledgements '08/05 OSSICP'08 Choco 18 / 25

22 Choco around the World Academic usage of Choco (as far as we know) in France : Universities : Nantes, Montpellier, Rennes, Toulouse, Clermont-Ferrand Engineering schools : ENSTA, Ecole des Mines de Nancy, Ecole des Mines de Nantes in Europe : UK : University of Glasgow Ireland : University of Cork '08/05 OSSICP'08 Choco 19 / 25

23 Choco around the World Industry usage of Choco (as far as we know) Big companies : Bouygues, Amadeus, Dassault Research agencies : ONERA, NASA Software and Integrators : Kls-Optim, alfaplan GmbH '08/05 OSSICP'08 Choco 20 / 25

24 The future of Choco Outline 1 The Choco constraint solver 2 The practice of Choco 3 Choco around the World 4 The future of Choco 5 Acknowledgements '08/05 OSSICP'08 Choco 21 / 25

25 The future of Choco Choco diusion A ChocoDay alongside the French CP days (in June) For the rst time : contestant within the CP solver competition A dynamic website : downloads, teaching material, demo material, etc. '08/05 OSSICP'08 Choco 22 / 25

26 The future of Choco Current hot topics inside choco integrating explanations (PaLM V2) implementing automatic reformulation techniques global constraint automatic and generic generation integration with LP! '08/05 OSSICP'08 Choco 23 / 25

27 Acknowledgements Outline 1 The Choco constraint solver 2 The practice of Choco 3 Choco around the World 4 The future of Choco 5 Acknowledgements '08/05 OSSICP'08 Choco 24 / 25

Acknowledgements The Choco team the founding fathers François Laburthe (Amadeus), Narendra Jussien (EMN, LINA) the core team Guillaume Rochart (Bouygues), Hadrien Cambazard (4C) the new generation

28 Acknowledgements The Choco team the founding fathers François Laburthe (Amadeus), Narendra Jussien (EMN, LINA) the core team Guillaume Rochart (Bouygues), Hadrien Cambazard (4C) the new generation Charles Prud'homme (EMN project management), Xavier Lorca (EMN teaching, training), Guillaume Richaud (EMN dev.), Julien Menana (EMN dev.), Arnaud Malapert (EMN dev.) the funding fathers École des Mines de Nantes, Bouygues SA, Amadeus SA '08/05 OSSICP'08 Choco 25 / 25

An introduction to Choco 3.0

An introduction to Choco 3.0 an Open Source Java Constraint Programming Library C.Prud homme, JG. Fages EMNantes, INRIA TASC, CNRS LINA Nantes, France 16 th September 2013 16 th September 2013 CPSolvers