XA - Introduction

Introduction

Overview

Welcome to the TOMLAB /XA User’s Guide. TOMLAB /XA includes the XA solver suite from Sunset Software Technology and an interface to The MathWorks’ MATLAB.

TOMLAB /XA is a solver package providing the user with functionality for solving linear, binary, integer and semi-continuous linear programming problems, as well as quadratic programming problems.

Contents of this Manual

• Section intro provides a basic overview of the TOMLAB /XA solver package.
• Section Using provides an overview of the Matlab interface to XA.
• Section options describes how to set XA solver options from Matlab.
• Section xaroutines gives detailed information about the interface routines {xa} and {xaTL}. The solver control options, branch and bound settings, as well as solver and model status codes are also explained in this section.

More information

Please visit the following links for more information:

• http://tomopt.com/tomlab/products/xa/
• http://www.sunsetsoft.com

Prerequisites

In this manual we assume that the user is familiar with linear, mixed-integer and quadratic programming, setting up problems in TOMLAB (in particular mixed-integer ({mip}) problems) and the TOMLAB language in general.

Using the Matlab Interface

The XA solver is accessed via the {tomRun} driver routine, which calls the {xaTL} interface routine. The solver itself is located in the library file {Xav14}. It is also possible to make a direct call the {xaTL} using the TOMLAB format, as well as a direct call to the solver interface by calling {xa}.

It is recommended that the TOMLAB format is used for maximum flexibility.

{3}{l}{\label{tab:interface}The interface routines.}
{Function} & {Description} & {Section}

{xa}& The interface routine calls the XA library. & xa

{xaTL}& The interface routine called by the  driver routine $tomRun$ or by a direct call. This routine then calls the interface routine xa, which calls the library file $Xav14$ & xaTL

Setting XA Options

All XA control parameters are possible to set from.

Setting options using the xaControl structure

The parameters can be set as subfields in the {Prob.MIP.xaControl}structure. The following example shows how to set a limit on the maximum number of iterations.

Prob = mipAssign(...)     % Setup problem, see help mipAssign for more information

Prob.MIP.xaControl.ITERATION = 20000; % Setting maximum number of iterations

The maximum number of iterations can also be done through the parameter {MaxIter}:

Prob.optParam.MaxIter = 20000;

In the cases where a solver specific parameter has a corresponding  general parameter, the latter is used only if the user has not given the solver specific parameter.

A complete description of the available XA parameters can be found in Section xaoptions.

IIS

Irreducible Infeasible Sets (IIS) can be found with TOMLAB /XA. There are two options available to the user. The first one delivers the infeasible rows from the last simplex tableau. The second one will try to find a minimal number of constraints that need to be removed or corrected to make the model feasible. There may be more sets that the one delivered. The inputs and outputs are explained in Section xaTL.