Paper on Xpress

I was asked to announce a paper on the Xpress solver:

Richard Laundy, Michael Perregaard, Gabriel Tavares, Horia Tipi, Alkis Vazacopoulos
Solving Hard Mixed-Integer Programming Problems with Xpress-MP: A MIPLIB 2003 Case Study
INFORMS Journal on Computing
Vol. 21, No. 2, Spring 2009, pp. 304–313

Xpress was recently acquired by Fair Isaac. I believe that for users of Xpress not much has changed as a result of this (may be their spelling of optimise will change, although it would be nice to have a recognizable British optimiser around.). The paper discusses some impressive progress on some notorious difficult MIP problems.

Note that the results are from three years ago! These type of performance review papers are usually already outdated before they  are actually printed; may be a printed scientific journal is not the optimal venue for a paper like this.

Bug in GAMS/Xpress link

The GAMS/Xpress link can terminate without reason:

**** SOLVER STATUS 4 TERMINATED BY SOLVER
**** MODEL STATUS 8 INTEGER SOLUTION
**** OBJECTIVE VALUE 134400.0000

RESOURCE USAGE, LIMIT 30.379 1000.000
ITERATION COUNT, LIMIT 5515 10000

The listing files does not convey any messages indicating the reason for stopping. We have observed this before, but this bug has not been fixed as of now. If a solver stops it is important to say why. Just simple-mindedly reporting "terminated by solver" makes it very difficult to fix whatever the reason is for the termination of the job.

Note: the log file did not help me either with information why the solve was stopped.