Can't get constraint, like 0 <= 1, by name

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ce jekl

2022年05月29日 10:40 編集済み

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I use

model.addConstr(x.sum(i, '*') <= 1, f"constr_{i}")

However, if x.select(i, '*') is empty, the constraint cannot be get by name.

m = Model()
c = m.addConstr(0 <= 1, "123")
m.update()
assert c is not None
cc = m.getConstrByName("123")
assert cc is None

How can I get this constraint? I want to keep the number of the constraints the same as my dict, so I can't just skip these trivial constraints.

PS: I found a workaround to this problem: just change the zero left hand side to LinExpr(0)

#c = m.addConstr(0 <= 1, "123")
c = m.addConstr(LinExpr(0) <= 1, "123")

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年11月16日 23:35

  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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  Eli Towle

  • Gurobi Staff

  2022年05月31日 20:52

  You could also pass the constraint name to Model.addConstr() using the \(\texttt{name}\) keyword argument instead of as a positional argument:

  c = m.addConstr(0 <= 1, name='c123')
  m.update()
  print(c.ConstrName)  # c123

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  ce jekl

  2022年06月10日 08:28

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  I think your point is interesting, with name keyword, getConstrByName works ok, however, it doesn't work without the keyword.

  m = Model()
  c1 = m.addConstr(0 <= 1, "c1")
  c2 = m.addConstr(0 <= 1, name="c2")
  m.update()
  assert c1 is not None and c2 is not None
  cc1 = m.getConstrByName("c1")  # cannot get c1
  assert cc1 is None
  cc2 = m.getConstrByName("c2")  # can get c2. Why?
  assert cc2 is not None

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  Eli Towle

  • Gurobi Staff

  2022年06月11日 02:58

  Right, I was suggesting a different workaround. We have logged this as a bug; thanks for reporting it!

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  ce jekl

  2022年06月11日 17:41

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  Thanks a lot!

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