Extra parameter in a callback function

[Laura Catalina Echeverri Guzmán]

Hello everyone,

I'm writting a callback function for a model but I need to access to an object that is not in the model (it is not a variable neither a constraint, it is a matrix that is not used to set the model).  I see there are just two parameters allowed in a callback function, model and where; but, what if I need to access (in the callback function) to a matrix to set a new lazy constraint? How can I do it?

Best regards,

Laura Echeverri

[Bjoern Simon]

Hello Laura,

If the matrix is not part of the Gurobi model, then you cannot access it from Gurobi; hence you need to get/access it from another object outside Gurobi.

Regards,

Bjoern

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[Andy Jaworski]

I am not sure is this is what you need, but you can auxiliary parameters to a Gurobi model.  Here is an example (I think you can find a similar example in Gurobi example codes) of my callback function:

def mycallback(model, where):

if where == GRB.callback.MIP:

time = model.cbGet(GRB.callback.RUNTIME)

objbst = model.cbGet(GRB.callback.MIP_OBJBST)

objbnd = model.cbGet(GRB.callback.MIP_OBJBND)

mipgap = objbst - objbnd

if mipgap <= model._gap and time > model._timelimit1:

print "termination 1"

model.terminate()

elif time > model._timelimit2:

print "termination 2"

model.terminate()

There are 2 different time limits and a gap parameters that have to be added to the model.

        m._timelimit1 = params1['timelimit1']

m._timelimit2 = params1['timelimit2']

m._gap = params1['mipgap']

Since I use this inside a Python function I pass the params1 dictionary to it from the outside.  It is simply

params1 = {"timelimit1": 300,

                 "timelimit2": 600,

                 "mipgap": 1}

I do not see why one of the parameters cannot be a matrix.

Hope this helps,

Andy

[RobbyD]

G'day Laura

From a .NET perspective this is an easy problem; in the declaration of the callback class, you simply pass the external data that you require access to in the callback routine. Eg:

Class MyCallback
    Inherits Gurobi.GRBCallback

    Private data1 As Object
    Private data2 As Integer

    Public Sub New(d1 As Object, d2 As Integer)
        Me.data1 = d1
        Me.data2 = d2
    End Sub

    Protected Overrides Sub Callback()

        Console.WriteLine(Me.data2)

    End Sub

End Class

I assume the other non-.NET options have something similar.
Cheers, Rob.

[Laura Catalina Echeverri Guzmán]

Thank you very much to all of you. 

In the end, as the matrix was defined outside the function callback, it behaved as a global variable for it, so I could access it, taking care to place the callback function in the right place.