One of our OpenSolver users recently worked with modelling guru Stu Mitchell to move his model from OpenSolver to SolverStudio. The OpenSolver model originally took 4 hours to solve. After simplifying the spreadsheet, this reduced to 2 hours. Stu created a SolverStudio version that solved the same problem in just 20 seconds. To quote our user: The conversion to SolverStudio has been an excellent improvement.
If you have a complicated spreadsheet, then you may also find that SolverStudio gives much better solve times. Furthermore, the latest SolverStudio release includes ready-to-run models for many common problem formulations, which helps make the conversion even easier. Give it a go, and let us know how you get on.
OpenSolver would not be possible without the CBC solver developed by the COIN-OR group. Working with colleagues Bob Fourer, Kevin Furman, William Hart and Michael Trick, we are preparing to nominate the initiators and founders of COIN-OR for the 2014 INFORMS Impact Prize. Thus we are soliciting testimonials to the impact that COIN-OR projects, and OpenSolver in particular, have had on diverse research and business activities.
This is a nice OpenSolver application that gave savings of $1.1M annually:
||Batching Outbound Shipments for Whirlpool Corporation
||Bertolino, Michele ; Herbst, Ana ; Jones, Andy ; Liem, Adam ; Nemes, Travis ; O’Gorman, Melanie ; Russell, Samantha ; Sood, Eric
||The team investigated the implementation of batch-picking shipments at a regional distribution center for Whirlpool Corporation, the world’s largest appliance manufacturer. An Excel-based optimization tool was created to strategically batch shipments to more effectively utilize carrying capacity of clamping forklifts across the network. Due to the decrease in labor hours, this resulted in savings of $1.1M annually.
Informs Transactions on Education has just published a special issue in honour of Paul Jenson who developed some excellent Excel tools for teaching operations research and management science. This special issue includes an article on SolverStudio. Cheers, Andrew
This guide, Practical Guidelines for Solving Difficult Mixed Integer Programs, might be useful for people looking for tips on how to solve difficult integer programming models.
I’ll be presenting on SolverStudio at the INFORMS conference in Minneapolis. Please come along to the Modeling Systems II session “MD08”, Monday Oct 07, 16:30 – 18:00, Level 2 – Room 200H to learn about SolverStudio, or to ask me OpenSolver questions! I look forward to seeing you there. Andrew
As a New Zealander and a yachtie, I have been watching the Americas cup racing with great interest as Emirates Team New Zealand races against Oracle Team USA. If you want to see incredible technology and dramatic sailing, check out http://americascup.com – Oracle have done a fantastic job at bringing this racing onto our TVs and browsers. And, Kiwis, don’t forget to wear your red socks… Andrew.
PS: You might also like to read: Philpott, A.B., Mason, A.J., ‘Optimising Yacht Routes under Uncertainty,’ Proceedings of the 15th Chesapeake Sailing Yacht Symposium, Annapolis, Maryland, p89-98, January 2001 (also available here).
My student, Matthew, has just succeeded in getting OpenSolver running with the NOMAD non-linear solver from the Gerad group. Many thanks to Jonathon Currie & David Wilson, creators of the OPTI Matlab toolbox (which also includes NOMAD), for letting us learn from your experiences in compiling this (and the COIN-OR code) under Visual Studio.
Matthew’s code is very much beta, but it shows that we can make it all work to get a powerful non-linear solver working with Excel. The challenge has been getting our VBA code to call the NOMAD C++ code which then has to call back into a thin C++ layer which runs our VBA code which re-calculates the spreadsheet for each new set of variable values; trivial, really! We initially created an XLL Excel add-in to help with this, but it turns out any DLL can do this using the Microsoft XLL interface libraries, so we now simply create a DLL that is linked into our OpenSolver VBA add-in.
Well done, Matthew, in getting this all to work, given minimal previous experience in C (and none in C++)! It’s a real privilege to work with such excellent Engineering Science students.
This will be released in the next beta version, coming soon….
Bernhard Aeschbacher (University of Zurich, Department of Business Administration) has just finished his Masters thesis on using OpenSolver for scheduling physicians. His thesis and Excel model are available here. It was great to see Bernard using OpenSolver’s on-sheet highlighting in his appendix to show how his model was built. Bernhard also gave me most useful feedback on a problem with non-English systems; OpenSolver 2.1 fixes this.
OpenSolver 2.1 is now released, and has a number of fixes and improvements. These include a newer version of the optimiser CBC, a bug fix for handling multiple cell blocks as decision cells on non-English systems, more robust non-linearity checking, and the ability to turn off this non-linearity checking if you know your model is linear. We now also display ≥ instead of > in our on-sheet constraints. All feedback is welcome.
Iain Dunning just sent me a link to Katherine Perry’s masters thesis on Call Center Scheduling Problem using Spreadsheet Optimization and VBA. (You will have to click past a broken certificate.) Katherine has been using OpenSolver to solve her call center problems. Her thesis includes an appendix giving step by step instructions on installing OpenSolver that might be useful for new users.
DEA Frontier, developed by Joe Zhu, is an Excel add-in for DEA Analysis. Joe has now released a version that works with OpenSolver, allowing larger models to be solved.
Fixed some display issues in the model dialog to give more compact displays, and force formulae RHS to be in absolute terms
Fixed a bug that saw models being wrongly built and then reported as non-linear (incorrectly) for some complex models if Excel calculation mode was set to manual.
Fixed passing of multiple parameters to CBC if the user defines a parameter table on the sheet; previously only the last parameter was passed.
Deleted the DLL’s downloaded in the .zip file which don’t seem to be needed now that we statically link everything in CBC.