Incorrect Result for single variable problem

回答済み

Varun Deshpande

2021年02月03日 07:02

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min z = -y

st. x-y >= 1, y <= 0, x + y <= 2

The solution to the problem must be 1. Can someone please explain this egregious result?

Thanks

import gurobipy as gp
m = gp.Model()
x = m.addVar(name = 'x')
y = m.addVar(name = 'y')
x = 0
m.addConstr(x -y >= 1)
m.addConstr(y <= 0)
m.addConstr(x + y <= 2)
m.setObjective((-1)*y, gp.GRB.MINIMIZE)
m.optimize()

Gurobi Optimizer version 9.1.0 build v9.1.0rc0 (win64)
Thread count: 2 physical cores, 2 logical processors, using up to 2 threads
Optimize a model with 3 rows, 2 columns and 3 nonzeros
Model fingerprint: 0x4470dc98
Coefficient statistics:
Matrix range [1e+00, 1e+00]
Objective range [1e+00, 1e+00]
Bounds range [0e+00, 0e+00]
RHS range [1e+00, 2e+00]
Presolve removed 0 rows and 1 columns
Presolve time: 0.03s

Solved in 0 iterations and 0.03 seconds
Infeasible or unbounded mode

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年06月23日 03:00 編集済み

  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 why not try our AI Gurobot?.
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  Silke Horn

  • Gurobi Staff

  2021年02月03日 08:50

  By default, all variables have a lower bound of 0. You should change the definition of y as follows:

  y = m.addVar(lb=-gp.GRB.INFINITY, name = 'y')

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  Varun Deshpande

  2021年02月03日 09:55

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  Worked. Thanks!!

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