Yet Another Simulation Add-In

Version History

Version 0.8  --  April 3, 2001

This was the first publicly-available version.

Version 0.9  --  July 3, 2001

This version was used by about 125 students at Rutgers in the Fall of 2001.  Follow this link for the version 0.9 user guide

Bugs Fixed:

In version 0.8, the random number seed could be reset whenever YASAI paused to see if the user wanted to abort, leading to non-repeatable behavior for large models or slow processors.

Version 1.0  --  January 15, 2002

This version includes fixes of bugs discovered in Fall 2001, and some enhancements suggested in the journal paper referee reports.

Features Added:

YASAI now attempts to guess how many scenarios you need, and gives you a choice of accepting its guess or specifying a different number; this feature also involved a redesign of the main dialog box.

A triangular distribution generator has been added.

GENTABLE allows its arguments to have different shapes, so long as the total number of cells match.

Bugs Fixed:

In version 0.9, output statistics for variables having a different number of observations than the sample size were usually wrong.

In version 0.9, the arguments to GENNORMAL were rounded to integers.

GENTABLE now conforms with the specification and does not require all data to be in columns.

In version 0.9, worksheets with names like "Simulation Output blah", where blah was non-numeric, could crash YASAI.

Run times were reported incorrectly in version 0.9.

When error values are returned, they are now "true" Excel error objects.

Link updating now takes into account that some browsers may rename the add-in file from .XLA to .XLS.


The information in the "about" box has been expanded and updated.

GENTABLE has been rewritten and should be a little faster.

Some redundant argument type checking code has been deleted.

The tab order and tool tips in the main dialog box have been tweaked.

Version 1.1  --  April 23, 2002

This was a substantial maintenance and feature enhancement release.

Features Added:

Output and Parameter names are now sorted alphabetically on the output report.

YASAI Functions are now accessible from the "Statistics" category of the Excel "Insert Function" dialog box.

The YASAI version, same-seed setting, and random number seed are now included in the output report.

Users may specify a random number seed without the "same seed" box being checked.

A confirmation box now appears if user tries to simulate a sheet whose name begins "Simulation Output".

Simoutput now interprets TRUE as +1, rather than -1. It also returns a value with the same datatype as it is passed.

Bugs Fixed:

Added message box preventing YASAI from running without first having an open workbook (previously, selecting YASAI with no open workbook crashed Excel).


Substituted L'Ecuyer's MRG32K3A random number generator for VBA's RND(), which is not very sophisticated. The MRG32K3A random number generator function is called YRandom().  This change should result in more robust simulation results, although simulations run significantly slower.  However, there are some savings in memory, because a potentially large array that had to be maintained to work around a RND() seed-setting bug in Excel 97 has been eliminated (see "bugs fixed" for version 0.8).

Version 1.15  --  March 15, 2005

A minor maintenance release focused on the issue of link repair. Excel insists on using absolute pathnames in the "links" it uses to locate user-defined functions, which causes no end of trouble.

Features Added:

Link repair is now attempted both on the internal link array and on worksheet formula text. This should reduce the chance that users will have to manually repair text links. Also, if Excel asks whether you want to repair links, it now no longer matters if one answers "yes" or "no".

We have created an experimental auto-installer program to simplify installation.  It takes care of deleting old versions of YASAI, and also tries to install in a fixed path that is likely to exist on most systems,"C:\Program Files\Microsoft Office\Office\Library".  This change should reduce the likelihood that files moved between different computers will need link repair.  The installer may need further refinement, especially in dealing with systems where YASAI has already been installed.

Bugs Fixed:

Link repair should now work under Office XP (see "link repair" under "features added"). The link repair strategy version 1.1 employed in Office 97 and 2000 did not work under Office XP. Text-based link-repair is also needed.

Version 2.0  --  February 2, 2007

A major release with significant new functionality and major bug fixes.

Features Added:

A wide variety of charts can be created from the most recent simulation. This capability was developed several years ago, but needed more debugging.

The install.xls file should make installation easier on many systems. This file replaces the less reliable version 1.15 auto-installer. [Note: due to subsequent problems, the installer was deprecated in 2008 and is no longer recommended.]

We have added a generator for geometric random variables.

Bugs Fixed:

Greatly improved handling of situations in which two or more outputs have the same name. Outputs with the same name are now correctly "pooled" into a single set of observations, whose observation count may exceed the originally specified sample size. This change involved restructuring some of the internal data arrays. Previously, having two outputs with the same name could crash YASAI.

Although it has been hard for us to test, we have made changes to make YASAI function better with non-English language versions of Excel. Specifically, YASAI will attempt to insert its menu options into the foreign-language equivalent of the "Tools" menu, for example "Outils" in French Excel.

We have corrected a bug that could result in inaccurate data on the "Simulation Output" sheets.

Version 2.1  --  February 24, 2010

A maintenance release with bug fixes and improved Excel 2007 compatibility.

Bugs Fixed:

Previously, SIMOUTPUTs with large means but zero or infinitesimal variance could cause YASAI to crash. This bug has been corrected, and YASAI simply reports a zero standard deviation.

In earlier versions, attempting to produce a chart in which all data series are deterministic and identical could cause a crash. This bug has been corrected, although the resulting charts are of course not very interesting.

Version 2.1 corrects two different bugs affecting models with more than 10 SIMOUTPUTs. Previously, models with 11 SIMOUTPUTs would run, but produce blank simulation reports. Models with 12 or more SIMOUTPUTs would crash YASAI. Both of these bugs have been corrected.

In Excel 2007, charts containing only a single histogram used to contain a malformed legend. This bug has been corrected, and a standard legend should appear. The bug did not affect Excel 2003 users.

In Excel 2007, the appearance of the Add-Ins ribbon has been altered. "YASAI Charts..." no longer appears twice. Instead, there is a single "YASAI" menu button which pops up two choices, "Simulation" and "Charts". The Excel 2007 Add-ins ribbon buttons are now created in a different manner from the Excel 2003 menu choices, and it is hoped the new procedure will be more robust.

Version 2.2  --  September 20, 2010

A minor maintenance release, fixing a bug introduced in version 2.1. Version 2.1 would crash if run on a sheet with no SIMOUTPUTs. This behavior has been corrected. As in Version 2.1, sheets with more than 10 outputs should work properly.

Version 2.3  --  July 26, 2011

Another minor maintenance release, improving compatibility with Excel 2010. Link repair for a downloaded YASAI spreadsheet would sometimes crash VBA under Excel 2010; this behavior has been fixed.

Version 2.4b  --  November 21, 2013

Preliminary version with Mac Excel 2011 compatibility.

Version 2.4  --  December 2, 2013

Version compatible with Mac Excel 2011 (while still maintaining full Windows Excel compatibility). The only functionality that does not work on the Mac platform is histogram charting (cumulative charting works). Histogram charting is disabled on the Mac due to an apparent Excel bug. This version also contains minor bug fixes.

Version 2.5  --  March 28, 2014

Improves compatibility with Excel 2013. When using earlier versions of YASAI with Excel 2013, the add-ins tab would often disappear from the ribbon, and Excel would have to be closed and restarted to make it reappear. This behavior, due to changes in the semantics of the ribbon interface, has been corrected.

Version 2.6  --  May 18, 2016

Compatible with Mac Excel 2016, although simulation performance is poor compared to other versions of Excel.  Introduces the new SIMPARAMETER function which should replace PARAMETER and makes it much more straightforward to test all possible combinations from different parameter lists.  Also introduces a lognormal distribution generator and various bug fixes. 

This, version, like version 2.5, is compatible with Windows Excel 2016, as well as all previous Windows versions of Excel.

Version 2.7  --  June 25, 2017

This version has the ability to simulate models with more than one worksheet, through a new "simulate all sheets" option in the simulation dialog box. The vertical axis of histogram plots is now a probability scale, and there were some bug fixes.

Version 2.7.1  --  October 8, 2017

This minor releases fixes an incorrect expression datatype in the workbook activate event handler.  It seemed to work fine on nearly all computers, but would occasionally throw errors.

Version 2.7.2  --  January 17, 2018

This minor releases fixes several bugs:

  • Models with more than 11 simparameters did not work properly.  This problem is now fixed.  Thanks to Teddy Boyce for pointing out the bug, diagnosing the error in the code, and providing some of the code to fix the problem.

  • Charts in which there was just one bucket or tick mark below 0 would have all their negative datapoints dropped or invisible.  Thanks to Tito Homem-de-Melo for finding this problem, which turned out to be due to counterintuitive and undocumented behavior in Excel's FLOOR function.  It is now fixed.

We have recently been observing very slow simulation performance in Mac Excel 2011.  We do not know the reason for this performance problem and it seems to affect all recent YASAI versions.  If anybody has a fix, please contact Prof. Eckstein.

Version 3.0  --  June 6, 2019

A major release with several significant new features, some minor enhancements, and some bug fixes.  The lion's share of the work was performed by Sohum Sanghvi, a Rutgers independent study student, over the Spring 2019 academic semester.  The new features are:

  • There is now a "dump internal data" option in the simulation dialog box.  Checking this option causes full sample data for all outputs to be dumped to a new worksheet ply at the end of each simulation.

  • YASAI has functions to automatically the scenario with the highest mean value of a given variable in a simulation output report, or the lowest mean value.  This functionality was contributed by a user, Teddy Boyce.

  • Hypothesis testing:  YASAI can now perform t-tests to evaluate the statistical significance of the difference between the sample means displayed in the output.

The bug fixes and minor enhancements are as follows:

  • Histogram charts have been re-enabled when using Mac Excel 2016 (but not Mac Excel 2011, where they are not properly supported).

  • Histogram and cumulative charts can be mixed in any order without corrupting the axis labels.

  • Internal time values are now represented differently.  This change is intended to prevent crashes on Macs configured for some countries outside the USA.

  • The code that adds and removes the YASAI functions from the menu bars and ribbons has been partially reworked.  When viewing a chart, applicable YASAI functions (creating more charts or hypothesis testing, but not simulation or scenario highlighting) are immediately available without having to switch back to viewing a worksheet.


Disclaimer: Since this Software is provided free of charge, the Software is provided on an "AS IS" basis, without warranty of any kind. The authors assume no responsibility whatsoever for its use by other parties, and make no guarantees, expressed or implied, about its quality, reliability, or any other characteristic.