Multiply scalar array with two-dimensional Mvar? (GurobiError: Variable is not a 1D MVar object)

Answered

Olaf Lehn Tranås

February 21, 2022 15:38

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Hi. I am trying to improve my runtime by using Mvar instead of scalar variabes. I have a descision variable with a second dimension (time), but constraint coefficients which are time-independent, so my constraint looks like:

 

model = gp.Model()
A = np.random.rand(len(N)) #(N coefficients)
b = np.random.rand(len(T)) #(T timesteps)
X = model.addMVar((len(N),len(T))) 

model.addConstr(A@X == b)

However, I do get an error: GurobiError: Variable is not a 1D MVar object.
The product A@X works when X is a parameter but not a variable,
so it seems like gurobi does not support this multiplication for variables? Is there another way perhaps?

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  Jaromił Najman

  • Gurobi Staff

  February 22, 2022 13:20

  Hi Olaf,

  I think the Knowledge Base article How do I multiply an array and a 2-D MVar object using the matrix-friendly Python API? should answer your question.

  Best regards, 
  Jaromił

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