Team realopt

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Overall Objectives
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Software
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Section: Software

BaPCod - a generic branch-and-price code

We develop the prototype of a generic branch-and-price code, named BaPCod, for solving mixed integer programs by column generation. Existing software tools (Minto, Abacus, Symphony, BCP, G12) are limited to offering “tool-boxes” to ease the implementation of algorithms combining branch-and-price-and-cut. With these, the user must implement three basic features for its application: the reformulation, the setting-up of the column generation procedure and the branching scheme. Other available codes (Gencol, Maestro) that offer more by default were developed for a specific class of applications (such as the vehicle routing problem and its variants). Our prototype is a “black-box” implementation that does not require user input and is not application specific. The features are

(i) the automation of the Dantzig-Wolfe reformulation process (the user defines a mixed integer programming problem in terms of variables and constraints, identifies sub-problems, and can provide the associated solvers if available, but he does not need to explicitly define the reformulation, the explicit form of the columns, their reduced cost, or the Lagrangian bounds).

(ii) a default column generation procedure with standard initialization and stabilization (it may offer a selection of solvers for the master) – the issue of stabilization is discussed in [1] , and

(iii) a default branching scheme – recent progress has been made on the issue of generic branching scheme in [20] .

(iv) default primal heuristics specially developed for use in a decomposition framework [33] .

The prototype software platform represents about 35000 lines of C++ code. It was/is used as background solver for 4 PhD thesis. It also served as the framework for our comparative study in a INRIA collaborative research action [1] . It has been experimented by two of our industrial partners, Exeo Solutions (Bayonne), on an inventory routing problem, and Orange Lab (France Telecom, Paris) on network design problems, and it is currently being tested by EURODECISION (Versailles). The prototype also enables us to be very responsive in our industrial contact. It is used in our approach to the powerplant planning optimization challenge proposed by EDF.


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