Conditional Constraints in Python: better error messages

回答済み

Victor Miller

2022年01月19日 19:35

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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.

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  Jaromił Najman

  • Gurobi Staff

  2022年01月20日 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

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