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Q&A’s –
Questions and Answers about VORSIM and VORSIM-built Models 1.
How is VORSIM
14 different from earlier versions? Version 14 has all of the virtues of
earlier versions such as: quitting a
model automatically switches you to the Solution Manager Control screen, when
you click the [Model] button on any control screen; you get a menu of saved
models, etc. Most important, VORSIM 14
runs in Excel 2000-2010. The control
screens have been redesigned a bit and some symmetry options have been added
to equation workbooks. 2. How is
VORSIM 15 different from version 14? Excel 2013 changed its file formats from *.xls to
*.xlsx for data files and *xlsm for files containing macros. VORSIM 15 accepts these changes and builds
upon them. In addition, VORSIM menus
were replaced by Tool screens. The
file nomenclature difference between versions 15 and 14 means that the
software and generated files do not work in the Excel version of the other;
e.g. VORSIM 15 will not work in earlier versions of Excel and VORSIM 14 will
not work in Excel 2013. However,
VORSIM 14 workbooks can be converted to VORSIM 15 nomenclature. 3.
Will models
built in an earlier version of VORSIM work in VORSIM 14? Yes, most
things should work in VORSIM 14 even though a few button positions and labels
may differ from those in earlier versions.
The only change really needed is the writing of indicator variable
names in the indicators workbook.
There you have to add either ! or [..] before your variable names if
you want to re-write indicators, however this a small editing change and can
be done in a few minutes. You also
might want to rebuild your solution file with the pull-down or Add-Ins menu
item of that name on the Solution Manager control screen. Send us your old model (vorsim@yahoo.com) if you have problems
running your older model in VORSIM 14 and we can help with any needed
conversions for a charge. Conversion
is also required to work with a version 14 and earlier model files in VORSIM
15. 4.
Can I build
large models in VORSIM? Yes models can easily be built with a few
thousand variables if needed. You can
also build a small model and expand and enlarge it later. There is a limit of 100 “change” and
“target” variables that can be entered; however in an economic model for
example, that can mean a maximum of 100 markets to be cleared BUT thousands
of equations can be used to model those 100 markets. If you do build a model with more than 100
change and target variables, you may need to purchase a larger Solver from
Frontline systems (see ‘Sources’). 5.
Is VORSIM a
model or a modeling system? VORSIM is a set of computer programs, which
help you build models using the Excel spreadsheet as a model platform, i.e.
it is a modeling system rather than a model.
The model you build will be set of Excel workbooks containing programs
for the control and simulation of the model.
As you build a model, you create separate workbooks for the definition
of your model structure and nomenclature, for the data, and for the model
equations. Solutions are saved as
named Excel workbooks. In addition
many other model related files exist as Excel workbooks. VORSIM guides your organization of all of
the information about your model in an efficient way. Each model has its own directory where all
relevant information is kept. As a
modeling system, VORSIM helps organize models and related information in the
Excel spreadsheet environment. 6.
Can I put
formulas (which calculate cell values from other cell values) into a data
workbook? Yes. Numbers (not formulas) are taken
from the data sheet for: a) entry into the Basedata sheet of the
equation/parameter workbook, and b) entry into the historical and exogenous
data workbooks that are created along with a model. For example, if your model requires say a
world trade balance, you can use formulas in the data workbook to achieve
this; but the numbers generated by data workbook formulas would be used for
model initialization. 7.
Sometimes
people cannot run VORSIM models that others have created. What is the problem? When working with a model in a drive or directory
other than the one in which it was created, models sometimes give a
compilation error (an Excel VBA error).
These errors occur because Excel linkages in your computer are
different than those in the computer where the model workbook was
created. However, the solution is
likely to be simple. Use the |Update
Links in Selected File| item in the VORSIM menu on the Model Manager control
screen to change the linkages. Also
you may need to re-created model or equation files on your computer – a
simple operation, provided you have backed up everything and can restore you
data and equations into your re-created workbooks. Models that come with VORSIM are not
configured for solution; you have to do that yourself buy pressing the
suggested configuration button on the model spreadsheet. This insures that the linkages to Excel on
your computer are used. If you give a
model to another VORSIM user on another computer, it is good practice to not
configure the model for solution – let the recipient do that. 8.
Can VORSIM be
used to build quarterly or monthly models? Yes, VORSIM can easily handle
models built with annual, semi-annual, quarterly, or monthly data. For
annual data, you simply enter the time period as an integer (e.g. the year);
however if you are building a non-annual model, just use 1, 2, 3, etc. for
your time periods. When you have finished building your non-annual
model, use the VORSIM menu in the Model Manager control screen to add quarterly,
semi-annual, etc. time tags to your model workbooks. You will have a
completely documented and readable model with appropriate time tags. 9.
Can I put
equation parameters outside of a parameter matrix? The line
above, the line below and columns to the right of an equation parameter
matrix are saved along with the parameter matrix. Therefore you can put parameters outside
the matrix, provided your parameters are adjacent to the matrix. Any information outside of the adjacent
area will be lost when the equation is banked and then restored. 10.
Are there
special problems with a very large model in VORSIM? The most
important thing to consider is the number of constraints (target cells) for
solution. The Excel Solver that comes
with VORSIM has a limit of 100 constraints for a model (even so, a model with
100 constraints, e.g. 100 markets to clear, can still have thousands of
equations). Therefore the limit of
model size is only the number of rows and columns available in the version of
Excel you are using. Keep in mind that
many model-building operations and model solutions are slower for large
models. 11.
Can I upgrade
my current version of VORSIM to version 14 or 15 without paying the full
purchase price for a download version?
No but VORSIM 14 and 15 are
very cheap. However if you have a
documented problem with version 15, we will fix it and give you a fixed copy
free of charge. 12.
How do I
diagnose solution problems with my model? Note any messages that occur
such as “infeasible solution”. This
may just mean that convergence criteria are too tight. Try solving the model and see if markets
clear – this sometimes happens even if the ‘infeasible’ message comes
up. Read about solution problems in
your Excel manual and the Frontline website.
Depending upon the message, there may be a Solver parameter that you
can change (use the Solver pull-down menu or reassemble the model and change
the parameters on the {Solver parameters} sheet. For example, you might need to apply
scaling to you model for solutions purposes (adjusts for widely different
change variable values in the solution process). If a change in a Solver parameter does not
help, the problem may lie with your model structure or parameters. Finally, there are some options which can
be used to constrain model variables to remain within a certain range. You also should try to use a master target
variable to keep your solver going on large models. 13.
Why can’t I
view at the VBA code for VORSIM so that I can edit it for my use? VORSIM is
written for Excel using VBA (Visual Basic for Applications), the macro
language of Excel. VORSIM is a
copyrighted program and those licensing it do not have legal access to the
code. From a practical viewpoint,
VORSIM programming is complicated and if we allowed users to change it, they
could easily make changes that would prevent VORSIM programs from working at
all. If you want to add your own VBA
routines to your VORSIM model, consult some of the publications cited in
sources for further information. You are
perfectly free to add programs of your own to model workbooks. 14.
Why won’t my
VORSIM-built model run in Excel? The first
thing to check is your security settings.
For example, Office XP has an extra security level for Visual Basic
Projects (a VORSIM-built model is such a project). Until you give Excel access to Visual Basic
Projects, you will not be able to attach the necessary programs to you model
for manipulation and solution. To do
this, go to the Tools Menu, find Macro and click on Security. This brings up a Security menu and you must
select high, medium, or low security options.
You cannot select the “high” option if VORSIM is to work at all. If you select medium security, you will get
a warning message when a VORSIM program is run (annoying but one can live
with it). To avoid this problem
completely, you need to select the lowest security level in for Excel
macros. Next, you must allow access to
VBA Projects. Select the “Trusted
Sources” tab and check both (if you have both) of the items at the bottom of
the menu: “Trust all installed add-ins and templates” and “Trust access to
Visual Basic Project”. Then from your
model equation (eqp) file, re-build your model. It will contain the correct programs for
solution. You can learn more about security
problems by reading the file on Excel security in this website. In addition if you are using McAfee
anti-virus program, you must permanently turn off real time scanning before
you install VORSIM. McAfee real time
scanning tosses out a couple of *.bas files that are required for model
building. 15.
I get an
error message when I try solving my model for the first time. What do I do? Most solver related problems like this
occur because the version of the Solver that comes with version 14 of Excel
does not handle VBA Solver commands properly.
First, make sure that the Solver Add-in is installed with Excel by
clicking on the Tools Add-in menu and select Solver Add-in. If you do not see the Solver add-in on the
menu, you need to re-install Excel with the manual option and make sure the
Solver gets installed. Once you have
the Solver installed it is usually found in the Programs/Office/ Library/
Solver menu. The VORSIM Solver.xla
file should be 647 KB. If your solver
is smaller than this, execute the Solver.exe program in your VORSIM
folder. This should install the
correct Solver (647 KB), backing up the existing one. If this program does not work, then
manually copy the 2 solver files in your VORSIM directory (Solver.xla and
Solver32.dll) to replace those in the Solver library under your Office
folder. Then re-build your model from
your equation workbook. If you are using VORSIM 15 you will automatically use
the accompanying solver so installation problems should not occur. Then you must deal with solver error
messages.. 16.
Sometimes
when a program creates a workbook, it stops without completing the routine. What could be wrong? When a VORSIM
program creates a new workbook, it formats the pages (sheets) for
printing. If your default printer is not
turned on, the program may stop; just turn on your default printer. 17.
I specified
my model with a lagged variable but did not actually use a lagged variable in
an equation. I created and simulated
the model. Next, I modified the
equation to include a lagged variable but the equation is NOT written
correctly when the model is created. What is wrong? Here is a situation where a time-saving feature
of VORSIM can cause a problem. The
FIRST time you create a dynamic model, VORSIM writes two history workbooks
(e.g. DEMOhist.xls and DEMOhist.sol) using the data available. These workbooks are NOT re-created when the
model is re-created. However they are
deleted when the Basedata is updated in the equation workbook. So if you later added the lagged variables
to equations, just update the Basedata sheet, re-write the equations, and
re-create the model (all click-of-the-button routines). 18.
I have some
small numbers in my database which seem to become zero when they are gathered
into the Basedata sheet of the equation workbook. I want these numbers to remain non-zero
when equations are written. How do I
deal with this problem? The answer
is simple; manually change the format for the relevant variables in the data
workbook. Data cell formats are
originally set in the definition workbook.
But once the data workbook has been created, they can be changed
manually. If numbers are smaller than
those anticipated when the data workbook was originally created, simply
manually change the formats with the Excel Format menu by increasing the
number of digits after the decimal point.
The format of a cell in the data workbook is also the format of the
cell in the Basedata sheet in the equation workbook. So once you have increased the number of
digits after the decimal point in the data workbook for small numbers, these
numbers should carry along into the equation workbook and be available for
use in equations. 19.
I set a
network printer as the default and all of a sudden I had problems creating a
model. I would get error messages and
the program would stop. What is the
problem here? VORSIM programs format files for printing (including the model file
itself) when they are created. If your
computer is connected to a non-local (i.e. network) printer and there is no
feedback from that printer, some programs may stop. The fix is simple, just set a local printer
as the default; preferably it should be the one attached to your computer’s
printer port but it might be another local one installed, such as Adobe
Distiller – which can receive print. 20.
Can I use IF
statements in model equations? Yes but
be careful. You can write equations
using the functions listed on the Variables sheet of the equation workbook,
but take care to check the required format of the function with VBA help; you
must have the correct syntax for the functions to operate properly. And remember, discontinuous functions may
lead to solution problems. 21.
I have a
problem with the SUMPRODUCT function in my model; I want to use
it so I don’t have to write long equations but sometimes it does not seem to
work. One form that does work in
VORSIM is as follows:
SUMPRODUCT((A5:A20)*(C10:C25)).
Put parentheses around the two ranges to be multiplied and use the
multiplication sign * between the two parenthesized ranges. 22.
I get the message “VORSIM locked for editing…” when I
try to operate on a model for workbook. This error occurs at times
when, in effect, two versions of VORSIM or a model file are open. One
solution is to close one of the files.
One problem with VORSIM 14 might
be that there are stray VORSIM files elsewhere than in the VORSIM directory
(or possibly there are more than one VORSIM directories created during
installation). One thing to try is to
uninstall and re-install VORSIM AFTER you have run the “Check Stray Files”
program in the VORSIM windows. This
will help you eliminate extraneous VORSIM files. To uninstall VORSIM, go to the VORSIM
directory and click the “unstall.exe” program to uninstall VORSIM. For recent versions of VORSIM, delete it
from the control screen delete programs option. Note that when it is deleted, desktop and
start menu icons may have to be removed manually. 23. Sometimes I
get a message “..is a read-only file..” when I am carrying out a VORSIM
operation on a model workbook. When files have been copied from another
source, often they are marked as ‘read-only’ to prevents them from being
changed. All you have to do is to go
to Explorer and right click on the file and choose its properties. Remove the ‘read-only’check and you will be
able to operate on it with VORSIM. 24. When I
replicate a model or when I create a data workbook with links to other files
(original data), I have a problem after a model is created; I am not able to
configure the model. What is wrong? The data
workbook can contain formulas BUT only formulas which relate to variables in
the data workbook. If the data
workbook contains formulas which link to another workbook, this causes
problems in writing the exogenous data file.
The solution is to remove the linkages to other workbooks in the data
workbook. This can be done by editing
the links or by loading the data workbook from the Solution Manager control
screen and using the VORSIM pull-down menu to remove ALL formulas in the data
workbook. You may want to keep a backup of the data workbook with the
linkages to other workbooks saved under another name. 25. Once I have
set the solver parameters in a model, can I change them? Once the
solver has been installed with the model, the solver parameters have been set
at the values you left in place on the solver parameters sheet. Furthermore, this sheet is removed from the
model. HOWEVER, if you unprotect the
model sheet and workbook, you can view the solver parameters menu you set by
using the Solver item on the Tools menu.
You can then change solver parameters on this menu and resolve the
model from the menu with the changed solver parameters. If you get a satisfactory solution, then
since this is equivalent to testing the solver by solving for the base
period, you should click the [Solve **mod] button to do a final model
solution. Note that testing the solver
while solving the model does not prepare a solution to be saved as a *.sol
file – this is done ONLY when solutions are obtained by the [Solve **mod]
button. 26. Can I use the
regular pull-down Solver menu to set solver parameters and solve my model? Yes, once the
[Test Solver] button has been clicked, the solver will be activated. First you MUST unprotect the model sheet
and workbook. Then you can click on
the Solver item on the pull-down menu and use buttons on it to change solver
parameters and solve the model. This
procedure does not save the parameters you set permanently but does use them
for model solution when you clock “Solve” on the menu. This is a good procedure for determining
the parameters for the Solver on your model.
Once you have satisfactory solver parameters, re-build the model,
permanently set the new parameters, and install the solver again. Remember that this method only solves for
one time period. You need to use the
VORSIM solve routine for a dynamic model which is solved progressively over
time. With VORSIM 15, procedures may
differ a bit. 27. How do I find errors in my model? There are several features of VORSIM which
can help you. First, when you write
equations in the equation workbook, some equation errors will be highlighted
as equation intercepts are calculated.
For example, a message saying that no data was found on the Basedata
sheet means that either a) the variable name was incorrectly spelled in the
matrix generating the equation or b) no data for the variable has been
entered into the data workbook (and subsequently copied into the Basedata
sheet in the equation workbook). A
message that no Basedata sheet data was found for a dependent variable means
just that – and the equation will not be written. You can visually check equations after they
are written to see that they are what you intended. You can also view the Excel version of the
equations in the B column – these should have only cell addresses, not
variable names. Finally, look at the
equation intercepts to make sure they make sense. For example, an equation which reads
“0*EUqtWHT…” has a zero intercept and will always give a zero value – often
this means that the equation has a syntax error – count your parentheses so
the number of left and right handed parentheses are the same. Sometimes a constant term value of 2007
means there is an equation problem.
When equations are written and the intercepts are calculated, the Excel
syntax is used and an unexpected intercept value usually means something is
wrong with the equation syntax (Excel interprets the incorrect syntax in a
way that yields an odd intercept value).
Finally, syntax errors can show up when equations are written into the
model. Sometimes equations are flagged
and the writing routine stops. When
all errors have been found and corrected and equations have been successfully
written into a model, there still can be errors which will cause solution
difficulties. The most common error is
that equation intercepts are wrongly calculated so that the base value
calculated by the model equation for a variable does NOT equal the base value
in the Basedata sheet of the equation workbook. The Model Manager VORSIM item - |Compare
Model with Basedata Values| - is very helpful in highlighting problems. It calculates a file of the difference
between the model base values and the Basedata values – any equation (yellow)
cell containing a non-zero value highlights a potential problem. If base values calculated by the model do
not equal Basedata values in the equation workbook, then the model will start
solving to find equilibrium BEFORE any policy changes have been introduced. In other words, the model does NOT start
from an equilibrium position. 28. What
improvements have been made in VORSIM 14? First, improvements from
version 12 have been retained.
Routines for model configuration have been improved. In one new option, you can place upper and
lower bounds on ‘change’ variables.
This can prevent model solutions that are “out of bounds” so to
speak. It can also shorten solution
time in large models. Another option
allows you to chose an overall target variable; this speeds up solutions for
some models. Other improvements have been
made in report writing and model management.
For example, you now can bring in equations from other models in your
current model under construction.
Finally, an option has been added to a model so that you can create
and use a time series based workbook of exogenous data for changing policy
variables for model scenarios. The
original option allows you to change one variable at a time while this new
option may allow you to operate on many variables in a sheet using normal
Excel methods. A utility has been
added which lists all of the models in the VMOD model directory. Menus additions include a routine to
convert solutions and exogenous data to a time series format. Most importantly, VORSIM 14 operates fully
in Excel 2007 - 2010. Helpers have
been added such as buttons to access the User’s Guide directly from control
screens. Finally, the VORSIM menus in
each control screen are accessed from the Add-Ins tab above the ribbon. More changes and improvements go into
VORSIM 15 and these are documented elsewhere. 29. Will VORSIM
14 operate correctly in Windows 7 and with Excel 2010? In Vista –
YES - VORSIM 14 operates normally in Windows 7. Downloading or executing the *.exe
installation programs may be confronted by the extra security embedded in
Windows 7 which may have to be temporarily relaxed. In Excel 2010 – YES - VORSIM 14 does
operate in Excel 2010. VORSIM
pull-down menus are found in the ‘ribbon’ structure (under “Add-ins”) which
replaces earlier Excel menus. VORSIM
has not been modified to change the ribbon structure in Excel 2010 but ribbon
functions are available in model workbooks just as VORSIM menu items
were. If you want model files
generated with Excel 2010 to be compatible with earlier versions, set the
Excel file saving option to save workbooks in a form compatible with earlier
versions of Excel (97-2003) rather than the Excel 2010 format (which is
different from earlier Excel versions).
If you operate VORSIM only in Excel 2010, then you should be able to
use its file system 30. When I try
to install the VORSIM Solver in Windows 7, I get a message that the
Solver.exe program does not run on a 64 bit machine. What do I do? The software that created Solver.exe works only for a
32 bit machine. However you can add
the solver manually with the following steps.
Find the Excel Solver folder (usually in the Microsoft
Office\Office12\Library\SOLVER folder or something like this). Rename Solver.xla to Solver.bak and Solver32.dll
to Solver32.bak. Then copy Solver.xla
and Solver32.dll from the VORSIM folder to the Excel Solver folder. This should do the trick. 31. When I try
to create a model I get an error “runtime # 9, subscript out of range”, what
is going on here? VORSIM has tried to execute a command which
uses a file name (which has been programmed in English) but does not
recognize the English word. If you are
used a non-English keyboard and input option, go into the control panel,
range and language options, and choose US English. Then VORSIM will again recognize its
English input and the message will disappear. 32. When I
install VORSIM, I get multiple copies of icons in the VORSIM Utilities
Window. Why? You probably
had an earlier version of VORSIM installed.
Installation may add new icons to the old set. You can either a) manually delete extra
icons (careful not to delete the wrong ones) or b) manually delete the icons
in the window and re-install VORSIM. 33. How have you
changed the Report Writer? As
before, the user designs reports. But
once a report (*.rpt) is saved, different methods of data transfer can be
used to put solution or other data into a report. Blocks of data can be copied with or
without a format, linkages to source data can be created in the report, or
movelists can be created to transfer data.
Once data blocks are put into a report, their source information is
kept in a comment in the block. Then
the sheet can be updated automatically with newer source data by simply using
the UPDATE… command in the VORSIM pull-down menu or Add-Ins menu to find and
recopy the source data. This
flexibility in methods of data transfer into a report will save considerable
time in report preparation. 34. Does VORSIM
work in Excel 2013? Yes with VORSIM 15! Yippee! This is explained on the VORSIM 15
website. Many changes were made using
Excel 2013 features. Model solutions
are more robust and obtained faster in VORSIM 15 than in VORSIM 14 or earlier
VORSIM versions. 35. Will models
build in VORSIM 14 or earlier versions work in version 15? Generally
yes, if key files are converted to the VORSIM 15 format and sheet linkages
are changed. The file nomenclature has
been changed in VORSIM 15, compared to versions 14 and earlier, hence
worksheets have to be renamed. The
Model Manager B button in the VORSIM 15 Model Manager control screen helps
you with this conversion. The [Modify
Links …] button lets you systematically change links from older VORSIM files
to the VORSIM 15 versions. |