Blog

OpenSolver for Google Sheets v2.2.0 (18 April 2016)

Today we are releasing OpenSolver for Google Sheets 2.2.0, which is a minor update with the following changes:

  • We have added support for early stopping in GLPK. If your problem is taking a while to solve and you are satisfied with the quality of the best solution that has been found so far, you can stop the solve and OpenSolver will load this solution into the sheet. To stop a solve early, just click the “Cancel solve and use current best solution” button.
  • When solving a “Target Objective” problem, we now try to minimize the deviation from the target rather than making the target a hard constraint. Previously, if the target was hard or impossible to reach, the solver may have taken a long time to finish. Coupled with the early stopping in GLPK, you can now stop the solve early if you see that the solution is close enough to your desired target. We will be adopting this approach in OpenSolver for Excel in the very near future.

If you already use OpenSolver for Google Sheets, the update will roll out automatically. If you are not yet a user, you can add it to Google Sheets using the link below:

As always, we welcome any feedback or ideas.

OpenSolver for Google Sheets v2.1.0 (15 April 2016)

Today we are releasing version 2.1.0 of OpenSolver for Google Sheets! This is a minor update that brings the following changes:

  • We have added support for the GLPK solver. You can now solve problems in your browser using the open-source GLPK solver, via glpk.js by Henri Gourvest. This solver runs in the browser on your computer rather than on a cloud server, so is typically much faster than the alternatives and we heavily recommend choosing it in place of Cbc via NEOS. Please let us know if you find this useful!
  • The linearity check now occurs before solving, in order to catch non-linearities before spending time solving the model. We recently changed the linearity check in OpenSolver for Excel to be much more robust and better at detecting non-linearity, and we are pleased to roll these changes out to Google Sheets as well.
  • Bugfixes:
    • Fixed bug where dialogs could time out before they finished loading.
    • Fixed sheet-scoping issue when storing constraints in multi-sheet models.

There is more information about the Google Sheets addon here on the dedicated page.

If you already use the addon, the update will automatically roll out. If you haven’t used it before, you can try it out here:

Update on Google’s Linear Solver

Google’s LinearOptimizationService has been fixed as of earlier today, so the Google Linear Solver should be working again. We are happy to now offer two additional solvers in case this happens again. It took over two weeks for Google to fix this bug, which is very frustrating for all of us, and hopefully is a problem we will be able to avoid in future!

Feedback and Issues

OpenSolver for Google Sheets is younger and less mature than the Excel version, so does not yet have the full range of features as in the Excel version. There are also a lot of possibilities that are created by the online aspect of Google Sheets (such as sharing sheets and multiple users on a sheet at once). This means there are many new features to consider and add to the addon as it evolves over time.

If you have any feature requests or experience any problems while using it, please let us know either here or by using the “Report an Issue” button inside Google Sheets (you can find this in “Add-ons > OpenSolver > Help”). If you use “Report an Issue”, please make sure that you include your contact details, otherwise there is no way for us to follow up!

We are always interested to hear how you are using OpenSolver, and in particular if you find the Google Sheets version useful (because we can”t count downloads, we have much less user information on the number of Google Sheets users). This allows us to balance the time we spend developing the Excel and Google Sheets versions according to user demand.

If you like the Google Sheets addon, please consider rating us in the store and/or leaving us a review, which will help other users find out about OpenSolver!

OpenSolver for Google Sheets v2.0 (7 April 2016)

We are very excited to announce the release of OpenSolver for Google Sheets 2.0! This is a major update that brings many improvements to the Google Sheets addon:

  • Support for one more than one model per workbook! Now, each sheet can have its own model. Use the sheet selector at the top of the sidebar to switch to the model for a sheet.
  • Models can reference cells on different sheets! You can define models using ranges on any sheet in the workbook.
  • Added a new solver: Cbc on NEOS! You can choose to either use the solver provided by Google, or the Cbc solver on the NEOS optimization cloud. Note that all problems submitted to NEOS become publicly available, please see the terms of use.
    , and use the new Cbc solver to solve models on the NEOS cloud server.
  • Support for resuming incomplete solves! If the solve takes more than 6 minutes, it will be stopped before a solution is found. Now you can resume the solve from where you left off, allowing you to solve larger models than before.

There is more information about the Google Sheets addon here on the dedicated page.

If you already use the addon, the update will automatically roll out. If you haven’t used it before, you can try it out here:

Update on Google’s Linear Solver

Last week, Google made breaking changes to their LinearOptimizationService inside Google Sheets, which means that it currently is not functional at all, and so we can’t use it in OpenSolver to solve optimisation problems. We reported the issue to Google immediately, but it has not been fixed at the time of writing this post. In the meantime, you should use the Cbc solver via the NEOS server.

If you would like to see Google fix their solver faster, you can click the star on the issue page linked before. The more stars the issue gets, the faster they will fix the problem.

Migrating models from previous versions of OpenSolver

Due to supporting one model per sheet, we have had to make changes to how we store the OpenSolver models, and so your current models are not automatically loaded into the new version. To load in your old model, you can either redefine it manually, or use the “Import previous model” item in the menu. This will load in your previous model as the model for the currently selected sheet.

Please get in touch if you have problems with this feature, we want to make the transition as smooth as possible for everyone. You should also use the “Show previous model data” menu item to open a box with the model information for your sheet. Please include this when you get in touch so that we can diagnose the problem.

Feedback and Issues

OpenSolver for Google Sheets is younger and less mature than the Excel version, so does not yet have the full range of features as in the Excel version. There are also a lot of possibilities that are created by the online aspect of Google Sheets (such as sharing sheets and multiple users on a sheet at once). This means there are many new features to consider and add to the addon as it evolves over time.

If you have any feature requests or experience any problems while using it, please let us know either here or by using the “Report an Issue” button inside Google Sheets (you can find this in “Add-ons > OpenSolver > Help”). If you use “Report an Issue”, please make sure that you include your contact details, otherwise there is no way for us to follow up!

We are always interested to hear how you are using OpenSolver, and in particular if you find the Google Sheets version useful (because we don’t control the downloads, we have much less user information on the number of Google Sheets users). This allows us to balance the time we spend developing the Excel and Google Sheets versions according to user demand.

If you like the Google Sheets addon, please consider rating us in the store and/or leaving us a review, which will help other users find out about OpenSolver!

Support for dynamic named ranges

One of the features that we have enjoyed in SolverStudio is support for dynamic ranges, i.e. named ranges that are created using formulae. OpenSolver 2.8 and later now supports this, and so you can use formulae to define ‘dynamic’ named ranges that are then used for the left hand side and right hand side of constraints, for the decision cells and for the objective. So for example, instead of having a constraint left hand side of A1:A4, you can defined a named range Constraint1LHS with a formula such as “=offset($A$1, 0, 0, COUNTA($A:$A),1)”. This range is dynamic in that it automatically expands as more values are entered into the A column. You can then set up a constraint in which you enter Constraint1LHS for the left hand side range. This means your model automatically works as the user changes the data on the sheet. For more information on dynamic range, see excel-easy.com or ozgrid.com. We hope you find this useful.

OpenSolver 2.8.2 Pre-release

We have just uploaded OpenSolver 2.8.2, available on our SourceForge site here.

This is a second attempt to work around the “Automation Error” bug that some users are seeing on some versions of Excel. (This appears to be caused by a VBA bug that is corrupting the cached code. We have now “cleaned” the code)

As always, please send us any feedback and let us know if you have any problems.

OpenSolver 2.8.1 Pre-release

We have just uploaded OpenSolver 2.8.1, available here.

This fixes two bugs with the 2.8.0 release. Some users may have encountered an “Automation Error” depending on their version of Excel, which we have now fixed. Additionally we have fixed an error that occurred when cancelling the “Set QuickSolve Parameters” dialog.

As always, please send us any feedback and let us know if you have any problems.

OpenSolver 2.8.0 Pre-release

We are happy today to announce the release of OpenSolver 2.8.0!

We will be releasing this first as a pre-release for wider testing before releasing it as stable in the near future. Anybody that has elected to receive update checks for experimental updates should get an update notification in the next day, otherwise the notification will come later once it is tested further (if you enabled the update checker).

You can download OpenSolver 2.8.0 Prerelease here.

This update contains a large number of bugfixes (the changelog lists over 30 major fixes!) as well as some new features. It fixes a lot of problems that users encountered in version 2.7.1. In particular, it fixes the compile error message “Method or data member not found” that some Mac users were encountering due to VBA becoming case-sensitive and treating Me.width and Me.Width differently. If you somehow still run into this message on the latest version, please let us know immediately so we can work with you to fix it.

There are a couple of changes to the way models are defined. First of all, it is now possible to define ranges in the objective, variables and constraint cells that are not on the same sheet as the model. Beforehand this was not consistently allowed, but now there should be no problems. NOTE: For the non-linear solvers Bonmin and Couenne that use our formula parser, the entire model needs to be on the same sheet due to limitations in the formula parser. This is something we want to fix as soon as possible.

The other big change to the way models are defined is that models can now be defined using named ranges. Now you can give names to ranges on the sheet and use these names when defining the model. For instance, if you have a named range “production” in A1:A4 and another named range “capacity” in B1:B4, instead of entering the constraint as “A1:A4 <= B1:B4”, you can now add it as “production <= capacity”. If the named range is changed to point to a different set of cells, the model will update and use the new set of cells when solving the problem. This change will allow for much more expressive power when creating models, and makes it easier to keep track of what each constraint means when defining the model.

We have also revamped the way we show the solver output when “Show optimisation progress while solving” is enabled. Previously we used a command prompt/terminal window to show the output from the solver, but now we do this inside Excel, along with an easy “Cancel” button to abort the solve. This is a much more stable way of doing things than before, and looks a lot nicer too!

The “About OpenSolver” form now indicates whether OpenSolver has been correctly installed, by which we mean all the files have been unzipped to the same place. If you are having trouble getting any solver to run, please make sure that this form says everything is correctly installed.

Finally, there are some minor changes to the API. We have removed the “GetObjectiveCellWithValidation” method, and have changed “GetObjectiveFunctionCell” to validate by default. A large number of the API methods have been altered to validate their inputs and outputs by default, which can be turned off. We have also added a host of new functions to go along with the ability to define the model using named ranges, which requires working with string arguments rather than ranges.

We appreciate any feedback you might have on the release, including the new features and any future features you might like. If you do encounter any problems, please either use the “Report Issue” button from inside OpenSolver, or leave a comment here so that we can address the problem.

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…”