model.addConstrs: Can't set variables equal to changing parameter?

Answered

Quentin De Boever

April 02, 2021 03:18

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Hi,

I have a VERY simple constraint I want to implement. Here's the general form:

x(t) + y(t) = A(t) for t = {1,4}

where x(t) and y(t) are variables. A(t) is a given vector/array. Can someone please show me how to implement this in Python (I'm using Jupyter Notebook)? I can't imagine it's difficult, but doesn't seem to work for me.

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• Official comment

  

  Simranjit Kaur

  • Gurobi Staff

  June 23, 2025 02:57 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?.
• 

  Eli Towle

  • Gurobi Staff

  April 02, 2021 03:30 Edited

  Below is a simple example that shows how to add two constraints of this form. You can make two calls to Model.addConstr(), or add both constraints at once in a single call to Model.addConstrs().

  import gurobipy as gp
  from gurobipy import GRB
  import random
  
  
  n = 5
  A = [random.random() for t in range(n)]
  
  m = gp.Model()
  x = m.addVars(n, name='x')
  y = m.addVars(n, name='y')
  
  # Option 1: two calls to Model.addConstr()
  for t in [1, 4]:
      m.addConstr(x[t] + y[t] == A[t], name=f'con[{t}]')
  
  # Option 2: one call to Model.addConstrs()
  m.addConstrs((x[t] + y[t] == A[t] for t in [1, 4]), name='con')

  I recommend looking at the Python API documentation and the functional code examples.

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  Quentin De Boever

  April 15, 2021 01:18

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  Thanks Eli! I got it working. I appreciate your help. Maybe you can help me on my other question?

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