# Difference between (addVars & addVar) and (addConstrs & addConstr)

Answered-
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 gp

m = 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 gp

m = 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,

Jaromił0 -
Thanks for a great explanation!

0 -
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

**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

0

Please sign in to leave a comment.

## Comments

3 comments