Conditional Constraints in Python: better error messages

Answered

Victor Miller

January 19, 2022 19:35

• 
• 
• 

It appears that MVars are not allowed in conditional constraints in the Python interface, but the error messages are rather mystifying.  For example

import gurobipy as gp

model = gp.Model()

avars = model.addMVar((10, 10), vtype=gp.GRB.BINARY, name='a')

svars = model.addMVar((10, 10), vtype=gp.GRB.BINARY, name='s')

model.addConstr((avars[0, 0] == 1) >> (svars[0, 0] <= 0))

gives the error message

AttributeError: 'MLinExpr' object has no attribute 'size'

If I then do

import numpy as np

tempa = np.array(avars.tolist())

model.addConstr((tempa[0, 0] == 1) >> (svars[0, 0] <= 0))

I get the error

TypeError: must be a real number, not MLinExpr

 

But if I then do

temps = np.array(svars.tolist())

model.addConstr(tempa[0, 0] == 1) >> (temps[0, 0] <= 0))

everything works ok.  I now undertand the current restriction that every variable involved in a conditional constraint must be a Var and not part of an MVar, but it would be really helpful if the error messages were not so cryptic.

0

• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  November 16, 2025 23:45

  This post is more than three years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.
• 

  Jaromił Najman

  • Gurobi Staff

  January 20, 2022 10:07

  This issue has been addressed in the latest Gurobi version. Which Gurobi version are you using? Could you please update to the latest version 9.5.0?

  Best regards,
  Jaromił

  0

Post is closed for comments.