Using the Enhanced Callback

Just as with the Solver Add-in, SolverWrapper allows for monitoring the optimization progress through a callback function. However, SolverWrapper improves on this by not only passing the callback trigger reason but also passing the trial number and the parent SolvProblem object for programming convenience. In order to activate the callback, one must set the following before running the SolveIt method:

    'pass the name of the user-defined callback function
    oProblem.Solver.UserCallbackMacroName = "ShowTrial" 'assumes ShowTrial function resides in ThisWorkbook
    'oProblem.Solver.UserCallbackMacroName = ActiveWorkbook.Name & "!" & "ShowTrial" 'if not in ThisWorkbook
    
    oProblem.SolveIt

The following illustrates an example callback function. The function must adhere to the following input arguments, and must return a Boolean specifying whether or not to stop Solver.

Function ShowTrial(ByVal reason As Long, ByVal trialNum As Long, oProblem As SolvProblem) As Boolean
    Dim i As Long
    
    If trialNum = 1 Then Debug.Print "Solver started on Worksheet: " & oProblem.SolverSheet.Name
    
    Debug.Print "Trial number: " & trialNum
    Debug.Print "Objective: " & oProblem.Objective.CellRange.value
    
    For i = 1 To oProblem.DecisionVars.Count
        Debug.Print oProblem.DecisionVars.CellRange(i).Address, oProblem.DecisionVars.CellRange(i).value
    Next i
    
    Debug.Print "Constraints Satisfied? " & oProblem.Constraints.AreSatisfied
    
    'decide whether to stop solver based on the reason for the event trigger
    Select Case reason
        Case SlvCallbackReason.slvShowIterations 'new iteration has completed or user hit esc key
            stopSolver = False
        Case SlvCallbackReason.slvMaxTimeLimit
            stopSolver = True 'if set to True then solver is stopped!
        Case SlvCallbackReason.slvMaxIterationsLimit
            stopSolver = False
        Case SlvCallbackReason.slvMaxSubproblemsLimit
            stopSolver = False
        Case SlvCallbackReason.slvMaxSolutionsLimit
            stopSolver = False
    End Select
    
    ShowTrial = stopSolver
End Function

Next Topic

Using SolverWrapper Events