addConstrs for X @ Q @ X

Chung-Yi Lin

January 29, 2022 21:29

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Hi,

I am using python 3.9

G is a sparse diagonal matrix.

Z = m.addMVar((nS,nT), vtype="C", name="Z", lb=-inf, ub=inf)

Err = m.addMVar(nT, vtype="C", name="Err", lb=0, ub=inf)

m.addConstrs((Err[t] == Z[:, t] @ G @ Z[:, t] for t in range(0, nT)),
             name="cErr")

I have no problem adding this constrain and solving the problem on my laptop with gurobi 9.1.2.

However, when I switch to my PC with gurobi 9.5, I cannot add this constraint. The error shows: 

GurobiError: Unsupported type (<class 'gurobipy.MQuadExpr'>) for LinExpr addition argument.

I think it is because the indexing change in the new release is shown in the Indexing of MVar and MConstr objects section of the Detailed Release Notes for Gurobi 9.5.

However, I still don't know how to translate the above constraint to fit the new version of the gurobipy API.

Thank you in advance.

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• 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.
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  Chung-Yi Lin

  January 30, 2022 15:50

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  I found myself adding the constraint in a very basic way

  m.addConstrs((Err[t] == sum(Z[s, t] * Z[s, t] * g for s in range(nS)) for t in range(0, nT)),
               name="cErr")

  If there is a smarter way to add such a constraint, please let me know.

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