Optimize Information Insight

進行中

Muhamad Fikri

2023年11月23日 12:58

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Hi,

I run my code to execute the NLP in an objective function (with linearization).

When I checked the optimized information, I got this detail

Optimize a model with 24 rows, 48 columns and 120 nonzeros
Model fingerprint: 0x962f7244
Model has 6 general constraints
Variable types: 12 continuous, 36 integer (36 binary)
Coefficient statistics:
  Matrix range     [1e+00, 4e+01]
  Objective range  [1e+00, 1e+00]
  Bounds range     [1e+00, 1e+00]
  RHS range        [1e+00, 6e+01]
Presolve removed 6 rows and 6 columns
Presolve time: 0.00s
Presolved: 18 rows, 42 columns, 114 nonzeros
Variable types: 0 continuous, 42 integer (36 binary)
Found heuristic solution: objective 58.5000000

What I wonder is the variable types, where the first one is
Variable types: 12 continuous, 36 integer (36 binary)

Then, the second one at the end before showing the Optimal solution found (tolerance ...)

The info is Variable types: 0 continuous, 42 integer (36 binary)

What does it mean?

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  Michel Soares

  2023年11月23日 18:02

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  Hi,

  The presolve step will usually change your model to another equivalent model that is easier for the solver to find a solution. In this step the number of constraints and variables are usually reduced ("Presolve removed 6 rows and 6 columns"), but new variables may also be added. The pre-solved model, in your case, has 18 constraints and 42 integer variables, 36 of them binary.

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  Muhamad Fikri

  2023年11月24日 07:53

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  Hi,

  Thank you for your response.

  So, in my case, this information means that at the initial stage, I have 12 continuous and 36 integers (36 binary). Then, it is reduced to 0 continuous and 42 integers (36 binary). Does it imply the model that I have is an integer without leaving any continuous on it?

  Also, how can I make the continuous variable keep being continuous?

   

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  Marika Karbstein

  • Gurobi Staff

  2023年11月24日 09:16

  In your example, some of the continuous variables are identified to be implied integers. So, there is an optimal solution where these variables take integer values.

  Also, how can I make the continuous variable keep being continuous?

  What do you mean? What do you want to achieve?

  Maybe the article How does presolve work? helps and gives some more insights.

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  Muhamad Fikri

  2023年11月24日 11:21

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  Hi,
  
  Thank you for the explanation.

  What I mean is I just want to know, if, in the initial stage, I have 12 continuous and 36 integers (36 binary). Then, the second one the continuous variable still exists. Not zero continuous like in this information (0 continuous and 42 integers (36 binary) ).
  I just want to understand the meaning of it.

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