Minimization Constraint not working

回答済み

Slade

2023年10月26日 14:51

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I have following constraint wish to be added into the optimization:

In python I coded as following:

I have a cell_map to keep the correct i sequence, and the i+1 is the next_i, I read https://support.gurobi.com/hc/en-us/community/posts/360074541152-How-to-write-a-maximize-constraint-using-gurobipy  and make the third term as a new constraint as constatint2 inner.

for cell_pair in cell_map:
    prev_i, i, next_i = cell_pair  # get neighboring cells
    if next_i != 0:
        for t in T:
            if i not in special_cells:
                # Constraint 2
                m.addConstr(a[next_i, t] == w / v * (N[next_i] - n[next_i, t]), name='constatint2 inner')
                m.addConstr(f[next_i, t] == min_(n[i, t], N[next_i], a[next_i, t]),
                            name=f"constraint2_{next_i}_{t}")

The problem is after I run the model and check the constraint with m.display(), only the 'constraint2 inner' is showing and the minimize constraint constraint 2 is not showing, after further checking the results, the constraint 2 is not working. Did I make any mistakes? 

 

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  Simranjit Kaur

  • Gurobi Staff

  2026年11月13日 01:35

  This post is more than two 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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  Riley Clement

  • Gurobi Staff

  2023年10月26日 22:56

  Hi Peirong,

  This may simply be a case of needing to call m.update() to update the model.

  However please note that the display() function is now deprecated and undocumented and we recommend that you do not use it.  The preferred way of inspecting a model is to write it to a LP file and then use a text editor to inspect the file.

  If you write it to a LP file and still encounter an obstacle then please let us know.

  - Riley

   

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  Slade

  2023年10月27日 01:04

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  Hi Riley,

  Really Appreciate your valuable suggestion. I believe the m.display() cause me the problem. Now with 

  m.write("myModel.lp")

  I can see the constraint 2 in the .lp file.

  General Constraints
   constraint2_1_1: f[2,1] = MIN ( n[1,1] , a[2,1] , 20 )

  Thank you!

  -Slade

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