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Integer Solution to Minimize Daily Cost does not exist

  • 16 May 2023
  • 2 replies
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Hi! I’m working on my small project and I’m a beginner in programming and AIMMS. 

I tried to run the model that I have developed but it resulted into “Warning: After zero iterations CPLEX 22.1 concluded that an integer solution to MinimizeDailyCost does not exist.” I attach my model and data.

I’m not sure where to start rectify this problem. Appreciate if anyone can help.

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Best answer by Marcel Hunting 19 May 2023, 16:40

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Userlevel 5
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Hi @Hazirah. I think that the integer variable NTUarea causes a conflict. There seems to be no feasible solution in which NTUarea can have an integer value. The model enforces NTUarea to take a fractional value but that is not allowed if this variable is declared as ‘integer’.

If you change the range of NTUarea into ‘nonnegative’ then CPLEX is able to find a solution, with fractional values for NTUarea.

Userlevel 5
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Hi @Hazirah,

I checked your model, and i have a few comments that may help you to find the infeasibility source. 

  1. Math Inspector (https://documentation.aimms.com/user-guide/creating-and-managing-a-model/the-math-program-inspector/a-worked-example.html#investigating-infeasibility) may be helpfull to find problematic constraints. 
  2. Add a | 0 to inactivate a few non-core constraints to minimize what can be causing problems (ie. capacity constraints).
  3. Take a double look on variables and constraints domains. Inconsistencies can cause solves to fail. 
  4. Make the use of inline variables (https://documentation.aimms.com/language-reference/optimization-modeling-components/variable-and-constraint-declaration/variable-declaration-and-attributes.html#variable-properties) to minimize this type of contraints: 

     

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