Lab 8
Solver In VBA
– Solver Add-in In Excel
► Solver Add-in In VBA
► Review
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Review: Using Solver in Excel
• Describe the optimization model on an Excel worksheet
• Open the Solver dialog box in Excel
(Tools/Solver)
• Specify the major items in the Solver dialog box
– Set Target Cell: the cell that contains the formula for the
objective function
– Equal To: the type of the objective function
– By Changing Cells: the cells set to contain the values of the
decision variables
– Subject to the Constraints: the adding of the constraints
– Options:
• Assume Linear Model
• Assume Non-Negative
– Reset All: clears all previous settings
• Run the Solver
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Using Solver with VBA Code
• Describe the model on an Excel worksheet
• Write code using Solver functions to specify the model.
The major Solver functions include:
–
–
–
–
–
SolverReset
SolverOk
SolverAdd
SolverOptions
SolverSolve
• Run the code
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Solver Functions in VBA
• Frontline Systems has written several VBA functions
that allow developers to operate Solver “behind the
scenes” with code
• These functions enable you to specify the model (target
cell, changing cells, and constraints) and set options,
etc.
• All the Solver functions begin with the word “Solver”
• Check the Web site www.frontsys.com/mlvbaref.htm
for detailed help on all Solver functions
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Setting a Reference
• To use the Solver functions in an application, you need
to set a Reference to the Solver Add-in in VBE.
• Set the reference with the Tools/References menu item
in VBE.
• In a long list of possible libraries of code, check
“Solver.xla” or “Solver”
• The reference will then appear in the Project Explorer
window.
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SolverReset Function
• To reset the Solver, use this line:
SolverReset
• It clears all previous settings.
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SolverOK Function
• It does three things:
– Identifies the target cell (Objective function)
– Specifies whether it is a maximization or minimization
problem
– Identifies the changing cells
• Syntax (it takes three arguments):
SolverOK SetCell:= , MaxMinVal:=, ByChange:=
If it is a maximization problem: MaxMinVal = 1
minimization problem : MaxMinVal = 2
• Example:
SolverOK SetCell:= Range(“E12”), MaxMinVal:=1, _
ByChange:=Range(“C9:D9”)
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SolverAdd Function (1)
• This function adds a new constraint each time it is called.
• Syntax:
SolverAdd CellRef:=, Relation:=, FormulaText:=
– CellRef is a reference to a cell or a range of cells on the active
worksheet that forms the left hand side of the constraint.
– Relation specifies the arithmetic relationship between the left
and right sides of the constraint. More specifically it has the
following values:
Relation
Relationship
1
<=
2
=
3
>=
4
the left hand side has integer value(s)
5
the left hand side has binary value(s)
(If the Relation equals to 4 or 5, the constraint has no right hand side.)
– FormulaText is the right hand side of the constraint, and it can
be a number or a reference to a range of cells.
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SolverAdd Function (2)
• Example:
SolverAdd CellRef:=Range(“D14”), Relation:=1, _
FormulaText:=“F14”
SolverAdd CellRef:=Range(“D15”), Relation:=1, _
FormulaText:=“F15”
SolverAdd CellRef:=Range(“D16”), Relation:=3, _
FormulaText:=“F16”
SolverAdd CellRef:=Range(“D17”), Relation:=3, _
FormulaText:=“F17”
• Or you can add several constraints together if they are of the
same relations:
SolverAdd CellRef:=Range(“D14:D15”), Relation:=1, _
FormulaText:=“F14:F15”
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SolverOptions Function
• It allows you to set any of the options and is
equivalent to click the Options button in the Solver
dialog box in Excel.
• Syntax:
SolverOptions (list of options separated by commas)
The two most frequently used options are the Assume Linear
Model and Assume Non-Negative options.
• Example:
SolverOptions AssumeLinear:=True, AssumeNonNeg:=True
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SolverSolve Function
• It is equivalent to click the Solve button in the usual Solver dialog
box to run the solver.
• Syntax:
SolverSolve [UserFinish:=]
– UserFinish: If it is True, the solver results dialog box will not appear;
if it is False or omitted, Solver displays the standard Solver results
dialog box, allowing the user to keep or discard the final solution
values, and optionally produce reports.
• The SolverSolve function returns an integer value that indicates
Solver’s success. If this integer is 0 (or 1, 2), it means successful; if
it is 4, the solver did not converge; if it is 5, there is not a feasible
solution.
• Example:
SolverSolve UserFinish:=True
Example of using the returned value:
If SolverSolve(UserFinish:=True) = 5 Then _
MsgBox “There are no feasible solutions.”
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Summary: Solving the Product Mix Example
• Putting the SolverReset, SolverOK, SolverAdd,
SolverOptions, and SolverSolve together, we can
write a sub to solve the product mix example:
Sub SaferlySolver()
SolverReset
SolverOK SetCell:=Range("E12"), MaxMinVal:=1, _
ByChange:=Range("C9:D9")
SolverAdd CellRef:=Range("E15:E16"), Relation:=1, _
FormulaText:="G15:G16"
SolverOptions AssumeLinear:=True, _
AssumeNonNeg:=True
If SolverSolve(UserFinish:=True) = 5 Then _
MsgBox "There are no feasible solutions. "
End Sub
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Add Buttons To Run VBA Code
• You can actually add form buttons on the Excel
worksheet so that users can simply click the Buttons
to run the VBA code:
– Anywhere at the Excel toolbar, right click to bring up a list
of toolbars available and select Forms tools
– Click on the fourth control – Button
– On the Worksheet – place and draw a button
– Assign the Solver Sub to this button
– Change the button label to “Run Solver”
– Write another short Sub in VBE to clear the results in
Range(“C9:D9”); assign this macro to a new button with
button label “Clear Results”
– Now click on the two buttons to clear the results and run the
solver in Excel!
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Assignment 2
Solve the Krazy Krakers’ spreadsheet model with
VBA code.
1) Consider the set up of the Krazy Kracker problem from
lab 2;
2) Write code with VBA Solver functions to solve the
Linear Programming (LP) model.
3) Within your codes, check to see whether there are
feasible solutions. If there are not, display an appropriate
message.
4) Add two Form buttons on the Worksheet to run the
solver and clear the results.
(Notes: Don’t forget to add the Reference in VBE before running
your Solver code)
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Note
• You are required to have both
assignments for this lab stay in one
excel file.
• Data and model of the two
assignment should be put in two
separate worksheets
• Create buttons for each
assignment.
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