Blog

INFORMS schedules conference volunteers using OpenSolver

http://meetings2.informs.org/wordpress/philadelphia/2015/11/04/optimal-student-volunteer-scheduling-for-the-2015-informs-annual-meeting/

“When we sat down to begin scheduling student volunteers for this year’s Annual Meeting, we recognized an opportunity to use OR methods to make the task more manageable. We realized that the problem consisted of scheduling 59 students across eight shifts (two shifts per day, four days), with each student required to work either one or two five-hour shifts (morning or afternoon). Since student volunteers are placed throughout the conference facilities, we decided to schedule students into the 74 “shift-location” combinations rather than simply assign a block of students into each shift.

A Doodle poll was set up to obtain student availability. Each student was asked to indicate five out of the eight shifts during which they were available. The availability data was translated into a cost matrix where the cost was zero if a student was available and a cost of 1,000,000 if a student was unavailable for a certain shift. The objective was to minimize the total cost of the assigned schedule, thereby creating a feasible schedule that did not assign any students to shift(s) for which they were unavailable.

The problem was set up and solved in MS Excel. The tool used was COIN-OR’s Open Solver add-in for MS Excel…”

New edition of Optimization Modeling with Spreadsheets by Kenneth Baker

Kenneth Baker is well known for his excellent introductory texts on optimisation modelling using spreadsheets. It is great to see that his latest edition of “Optimization Modeling with Spreadsheets” (ISBN: 978-1-118-93769-3, July 2015) now includes an online appendix on OpenSolver. I look forward to seeing a copy of this new edition when it arrives. Andrew

OpenSolver 2.7.1 (28 June 2015)

We have just released OpenSolver 2.7.1 which fixes a number of bugs in the 2.7.0 release. Please upgrade to this version if you are using 2.7.0 (or enable the update checker in OpenSolver to get automatically notified of these changes!).

Note: Unlike earlier versions of OpenSolver, we now correctly pass to the solvers (including CBC) the “Maximum number of iterations” value in the Options dialog. Be sure to set this (and the time limit) to a large value if want to find optimal solutions.

Great Maersk/OpenSolver presentation

I am on sabbatical at DTU in Denmark, and just enjoyed meeting Aleksandr from Maersk in Copenhagen who is doing some great work with OpenSolver (and perhaps SolverStudio in the future) to help make better decisions at one of the world’s largest shipping companies. Aleksandr presented some very sophisticated OpenSolver models, and is one of the few users I know of who uses the Quick Solve feature. (Any more of you out there?) Thanks, Aleksandr, for a great talk, and giving us some challenging models to think about as we plan for faster solve times in future releases. Andrew

OpenSolver 2.7.0 (16 June 2015)

Today we are happy to announce the release of OpenSolver 2.7.0, available for download here. The release fixes a large number of bugs and also introduces some great new features:

  • Update Checker: OpenSolver now includes an automatic update checker that will periodically check for updates. This is an opt-in feature that we hope will make it easier to keep up with the latest releases. As a side effect, we plan to move to more frequent releases so that new features and fixes are available sooner. More info on the Update Checker is available here.
  • VBA API: We have created a complete VBA interface to OpenSolver that allows full control of OpenSolver using VBA, much like Excel Solver’s API. We strongly recommend using these new functions to control OpenSolver instead of the Solver functions. The full list of API methods is here.
  • Error Reporting: We have revamped the error handling within OpenSolver to give us much more information when an error occurs. There is also an option to report issues from within Excel when an error occurs. This will email us directly with full information about the error, which will hopefully make it easier to resolve any issues you might encounter.
  • All solvers now support extra parameters being defined, and these parameters can now be set from the Options dialog. More information about using these parameters is here.
  • Highly experimental support has been added for the NOMAD solver on Mac. This feature is very new, so if you try this out please let us know how it goes.

We have also updated the included solvers to the following versions:

  • CBC 2.9.4
  • Bonmin 1.8.1
  • Couenne 0.5.3
  • NOMAD 3.7.2

As always, please let us know how you find the new version, and we appreciate any feedback you can offer.

False Positive with Virus Checker

We had a report yesterday from a user Daryl that BitDefender was reporting a possible virus infection on his PC that appeared to be connected with OpenSolver. Thanks to great work by Daryl and our programmer Jack, we identified this as a false positive (i.e. an incorrect report of a virus) being triggered by BitDefender’s ‘heuristics’. BitDefender was objecting to some of our VBA code, including one of our comments. (Note that I said comment, not actual code, and so this is definitely a case of BitDefender being overzealous!) We will tweak our next release to better avoid false reports such as these.

Thanks, again, to Daryl for contacting us with his concerns. Much appreciated.

Andrew

OpenSolver 2.6.1 (15 Feb 2015)

We are pleased to announce the release of OpenSolver 2.6.1. This release contains numerous bugfixes, as well as some new features:

  • Bonmin, Couenne and Gurobi support options set in OpenSolver (e.g. time limit, tolerance)
  • Gurobi now supports extra parameters just as CBC does (see http://opensolver.org/using-opensolver/#gurobi-params)
  • Support for more formulae in the non-linear solvers. SUMIF is now supported.
  • We have updated the COIN-OR solvers included with OpenSolver to CBC 2.9.0, Bonmin 1.8.0 and Couenne 0.5.1
  • The issues with OS X Yosemite have hopefully been resolved

Please let us know how you find it. In particular we are always interested in feedback on the OS X version, which should be a lot more robust now.

SolverStudio: 2 hours becomes 2 minutes

This user feedback helps summarise why we created SolverStudio, our free tool for Excel users that want to build bigger optimisation models:

Dear Andrew,
Couple of months ago you had advised me to solve [my OpenSolver] model (which takes 1.5 hours to even create set up file) in SolverStudio.

I followed your advise and now I would like to share my real life experience about such a big model.
While OpenSolver was solving my large problem in 2-2.5 hours (including setup and solution), SolverStudio GAMS formulation reduced the solution time to 2 minutes. I’d like to take this opportunity to thank everyone who developed such a tool. Also, SolverStudio greatly quickened up NEOS solver use. It was kind of painful to NEOS solver on its own…