Thanks to John Gregory and others at CPLEX I was able to resolve
problems I was having with CPLEX 7. I found out that big performance
declines can be caused by the existence of artificially large upper
bounds particularly on the objective function and the new CPLEX feature
that on restarts it automatically goes to the dual simplex algorithm.
Namely to find unboundedness at some point I put in the bound
profit.up=10000000; If you find restarts (second and subsequent solves)
to be very slow then remove such bounds (removal causes a reduction in
solution time from hours to seconds). You also could use the CPLEX
option file options
lpmethod 1
pdswitch 1
startalg 1
GAMS corporation has worked with others to create a new web site called http://www.gamsworld.org/. This web site contains quite a lot of material on Mixed Integer Nonlinear Programming (MINLP) but also has material on conversion to other languages such as AMPL and MPS format. A link to NEOS through the converter section (GAMS2XX) also allows one to submit jobs for solution on the NEOS computers.
GAMS has recently introduced a presentations and contributed documentation web page on http://www.gams.com/presentations/. Look there for papers on GAMS use and some instructional materials including some of the things I generated for past newsletters. Also see the Erwin Kalvelagen report on solving large MIP's with CPLEX on http://www.optimization-online.org/DB_HTML/2001/06/352.html.
Basic material appears, among other places, in the Rosenthal section in the GAMS manual or on http://www.gams.com/docs/gams/Tutorial.pdf; in the primer by Rob Delink and Judit Szőnyi on http://www.sls.wau.nl/enr/; in McCarl and Spreen Chapter 5 http://agecon2.tamu.edu/people/faculty/mccarl-bruce/mccspr/new05.pdf; in basic materials by me on http://www.gams.com/mccarl/aggamint.pdf; or Rardin's http://gilbreth.ecn.purdue.edu/~rardin/gams/notes.html. CGE materials are on Rutherford's http://www.mpsge.org/mainpage/mpsge.htm , on the GAMS presentations web page within documents by Loftgren, Delink and Szőnyi; on the MPSGE page http://www.gams.com/solvers/mpsge/ . Other materials are on http://www.gams.com/presentations/ including ones in Russian and Spanish.
I teach Basic GAMS in College Station, Texas November 5-8, 2001 (note this is a change from the earlier announced time ) and Advanced GAMS in Texas in January 7-10, 2002. Further information and other courses are listed on http://www.gams.com/courses.htm.
A topic of interest to many is the link between GAMS and other programs. I will be covering such topics here and in subsequent newsletters. For now I provide a document on how to develop an EXCEL spreadsheet that runs GAMS in the background. The document is on http://www.gams.com/mccarl/excelgams.pdf and the associated spreadsheet and GAMS file are on http://www.gams.com/mccarl/excelgams.zip. Later look for material on links when GAMS is in charge, Delphi, databases, graphics programs and put files. Also see the general treatment covering spreadsheets, databases in http://www.gams.com/interface/interface.html, Tom Rutherford's graphics and spreadsheet tools on http://www.mpsge.org/inclib/tools.htm or Uwe Schneider's graphics tools on http://www.uni-hamburg.de/Wiss/FB/15/Sustainability/schneider/gnuplot/.
To remove your name, please send an email to
mccarl@gams.com containing unsubscribe on the
subject line or unsubscribe through the web form http://www.gams.com/maillist/newsletter.htm.
This newsletter is not a product of GAMS Corporation
although it is distributed with their cooperation. August 15, 2001