Infeasible Model - IIS understanding
AnsweredHi,
I am very new to gurobi and I have a question on understanding the output of the model.IIS()
it returns three constraints that are only by themselves not conflicting:
\ Model _copy
\ LP format - for model browsing. Use MPS format to capture full model detail.
Minimize
Subject To
y=x-origin[1]: - x[1] + y[1] = -5
z_i_=_x_-_H_i[1]: - x[1] + z[531] = -9.997177124023438
y_@_y_<=_eps^2: [ y[0] ^2 + y[1] ^2 ] <= 1
Bounds
x[1] free
y[0] free
y[1] free
End
Since x1 = 5 would possibly a choice on which all these constraints would be satisfied if there is not another one that is conflicting, but that should be then included right?
Below is my model definition if that helps.
Thanks in advance!
Best
Tom
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Official comment
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Gurobi Staff
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Unless otherwise specified, the default lower bound on a variable in an LP model file is \( 0 \). So the model file really includes a fourth constraint/bound: \( z_{531} \geq 0 \). If you set \( x_1 = 5 \), then \( z_{531} \) must be negative (by the second constraint), which violates this lower bound.
Note that the default lower bound on variables added with Model.addMVar() is \( 0 \). This is also true for the Model.addVar() and Model.addVars() methods. To add variables with no lower bound, add the argument \( \texttt{lb=-GRB.INFINITY} \) to the method call.
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Thank you very much!
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