ILOG Solver Directions

1
ILOG Solver Directions

• Laurent Perron
• ILOG SA

2
Outline

• Constraint Programming, a powerful technology
• The CP suite in ILOG
• CP faces new challenges
• Recent Technical Advances

3
Constraint Programming, a Powerful Technology

• I hope this will be demonstrated by the workshop
• CP is a robust technology with a past of
  successful applications
• Some famous academics success in the OR community
  (10 teams problem closed easily)
• A large collection of deployed industrial
  applications based on Constraint Programming

4
CP Strengths

• A high level modeling language allows for a rich
  and accurate representation of the model
• Domain expertise is captured through a rich
  search language
• Special techniques (decomposition, LNS, repair)
  allows the tackling of large and difficult
  problems
• A clever tool for clever people

5
CP weaknesses

• A high level modeling language allows for a rich
  and accurate representation of the model
• Domain expertise is captured through a rich
  search language
• Special techniques (decomposition, LNS, repair)
  allows the tackling of large and difficult
  problems
• You need clever people to use this clever tool

6
ILOG CP Suite

• ILOG Solver
• Generic CP System
• ILOG Scheduler
• Detailed Scheduling Specialization
• ILOG Dispatcher
• Vehicule Routing and Disptaching Specialization
• ILOG Configurator
• Configuration System

7
ILOG CP Market

• ILOG CP Market is defined by
• ILOG Consultants
• Big ISV
• Specialized Solution Vendors
• Technical Consulting Companies
• Big Companies with Dedicated RD
• This is not a huge market
• We want to enlarge our market

8
CP Meets New Challenges

• To reach our goals, CP should be improved
• At the evaluation phase
• Easier to use tools
• Rapid results
• Low coding effort
• At the implementation phase
• Low technology profile
• At the maintenance phase
• The application should improve with time

9
New Rules for Tools Evaluation

• People are not very technical
• Maybe one week of training
• They may have a limited OR background
• The know basic OR rules about modeling
• They may not be Computer Science experts
• The cp system should be easily integrated/document
  ed
• Maybe not keen with compilers and library

10
News Rules for Evaluation (2)

• Evaluation Phase is Limited in time
• IT is made against other competing techniques
• And sometimes against internal tools
• We need to achieve something soon
• Even if the problem is over-constrained
• Even if the data are dirty
• Even if the model is naive

11
New Rules for Application Development

• The IT guy is not the OR Expert
• The code will not evolve
• The time devoted to Optimization is usually
  limited
• Users will need guidance
• Why this doesnt work?
• Users expect performance to improve with time
• Without code evolution

12
Usability

• To be effective, a CP solution consists of
• A good model
• A clever search part
• We would like to remove the need for search part
• At least for small problems, typically the one
  encountered in the evaluation phase

13
Robustness

• Different logically equivalent formulations can
  lead to different runtime performances
• Expand a global constraint into smaller subparts
• This imply that getting a good model is an art
• We do not believe this cannot be
• The CP Solver should detect these cases and
  reformulate the model
• Users do not know about different level of
  propagation

14
Evolution of the Code

• In the past, to use a new technology, a new
  constraint or a new search construct was
  implemented
• Users had to rewrite their code in order to
  benefit from it
• And new users had to learn more each time

15
Interactivity

• Users want Explanation
• And useful explanations
• Users want Solutions
• Even with over-constrained problems
• Along with explanations of why some constraints
  are not part of the solution

16
ILOG Solver Directions

• Default Search
• Model Reinforcement
• Constraint Aggregation
• Various work on robustness
• Better constraints (without filtering levels)
• No pathological cases
• No slow propagation
• Explanations and Solver Anyway

17
ILOG CP Directions

• There is a new suite of optimization tools in
  ILOG
• ILOG Plant Power Ops for production planning and
  scheduling
• ILOG Transport Power Ops for routing and
  dispatching
• ILOG Fab Power Ops for semi conductor industry