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## Comments

3 comments

• Gurobi Staff

The addVar method adds a single variable while the addVars method adds multiple variables at once. The addVars method is a convenience method, since you can get the exact same result by using a $$\texttt{for}$$-loop and the addVar method.

import gurobipy as gpm = gp.Model()x = m.addVars(3, name="x")m.update()print(x)

generates 3 variables named $$\texttt{"x[0]","x[1]","x[2]"}$$, which can be accessed via $$\texttt{x[0],x[1],x[2]}$$.

The equivalent code using addVar would be

import gurobipy as gpm = gp.Model()x = {}for i in range(3):    x[i] = m.addVar(name="x[%d]"%i)m.update()print(x)

The same difference holds for addConstr and addConstrs. There should be no significant performance difference between the two respective methods.

Usually, adding sets of optimization variables through addVars results in a more concise code.

For constraints, it is recommended to use addConstr if the generated constraints are very complex, i.e., when many $$\texttt{for}$$-loops and $$\texttt{if}$$-clauses are needed to iterate through the indices. Otherwise, using addConstrs to add a set of constraints simultaneously results in a more concise code.

You could browse through the Python examples to get a feeling when to use which method. Our webinar on gurobipy should also bring some clarity.

Best regards,
Jaromił

Thanks for a great explanation!

Jaromił Najman already gave a details answer. Thanks.

I just wanted to say one little point (that I keep in mind when it comes to addConstrs vs addConstr)

If you see the following model, the 3rd constraint is a single constraint (use addConstr) whereas 2nd constraint equation will become len(A) numbers of constraints. When we enumerate Equation 2 using index of decision variable x_ij, we get multiple constraints; in such case, lets use addConstrs.

https://or.stackexchange.com/questions/1508/common-structures-in-gurobi-python

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