Python API: Using single component of a MVar object in a non-matrix constraint

Answered

Marco Corrao

May 01, 2021 11:28 Edited

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Hi 

I only recently started working with the  Python API (Gurobi 9.1), which support matrix friendly modelling. Particularly, I have a problem that is naturally expressed in terms in matrix/vector form. say that I have a Mvar variable in the form:

\[\mathbf{x}=[x_1,x_2,...,x_N]^T\]

I would like to add a piecewise linear constraint in my problem in the form:

\[y=f(x_i)\]

where \(x_i\) is a single element of vector \(\mathbf{x}\). It seems that using x[i] as the xvar attribute of function GRBModel.addGenConstrPWL() returns an error,  so I was wondering whether there is any way to work around this in the Python API that allow to treat elements of a Mvar as standard scalar variables. If not, can I check whether the Matlab API would instead support this kind of statements?

Thanks advance,

Marco

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 02:55 Edited

  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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  Jaromił Najman

  • Gurobi Staff

  May 03, 2021 07:45 Edited

  Hi Marco,

  You could try to convert the \(\texttt{MVar}\) object to a nested list of Var objects via

  mvars = m.addMVar(10, name="myMVars")
  mvars_as_vars = mvars.tolist()
  m.addGenConstrPWL(mvars_as_vars[0], mvars_as_vars[1], [0,1,2], [1.5,0,3], "myPWLConstr")

  You will have to use the latest version of Gurobi to make it work as described above.

  Best regards,
  Jaromił

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  Marco Corrao

  May 03, 2021 14:49

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  Great, this works! Thanks a lot for your help.

  Best

  Marco

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