在 Python Gurobi 中删除变量

Question

I am using Python/Gurobi to optimize a problem. I generated variables using GRBaddVar through this code:

x[1,i,j,t] = model.addVar(vtype="B", name="x(1,%s,%s,%s)" % (i,j,t)) 

I also want to remove some variables in order to save some space. The variable is removed when a certain condition is true. Suppose the condition is when R = 1. To remove the variable I use the following code.

if R == 1:
    x[1,i,j,t] = model.delVars(vtype="B", name="x(1,%s,%s,%s)" % (i,j,t))

However, it resulted in the following error:

AttributeError: 'gurobipy.Model' object has no attribute 'delVars'

I have no idea what's wrong with the code since I just follow the documentation (attached below) from Gurobi. Thanks for your help!

Answer 1

As David noted, you are looking at the documentation for the C API.

In the Python API, you can remove a single variable with the Model.remove() method, using the Var object the argument. Eg,

model.remove(x[1,i,j,t])

You can use this same method to remove, eg, a list of Var objects at once.

Note that you should call Model.update() before removing variables in this manner.

Answer 2

"You can use this same method to remove, eg, a list of Var objects at once." Can anyone suggest how to remove multiple variables at once. I have the variable to be removed in a dict/list format. I am trying to the below code, but error appears: GurobiError: Item to be removed not a Var, MVar, Constr, MConstr, SOS, QConstr, or GenConstr

model.remove(var_to_remove_dict.keys())