Discrepancy in Objective Function Value Calculation

Awaiting user input

Marith Zeelenberg

• May 04, 2024 08:43

Hi,

I'm experiencing a discrepancy in my optimization model's objective function value and its expected value after solving with Gurobi. My objective function is defined as revenue minus total costs. However, when I calculate the expected result based on individual cost components and revenue, I get a different value from what Gurobi reports.

Here's my objective function:

```python
model.setObjective(
    revenue - total_costs,
    sense=GRB.MAXIMIZE)
```

These are my output values after solving the model:

- Fixed costs: 500000
- Additional capacity costs: 7770.0
- Operational costs: 155400.0
- Charging costs: 171.05
- Total costs: 663341.05
- Total revenue: 280383.04
- Objective function value: -385565.56

When I calculate the expected objective function value as `revenue - total costs`, I get:

280383.04 - 663341.05 = -382958.01

This differs from the value reported by Gurobi, which is -385565.56. The difference is around 2607.55. I'm trying to understand why this discrepancy exists.

What might be causing this difference between my calculated objective function value and what Gurobi reports?

Any insights or suggestions to resolve this discrepancy would be greatly appreciated. Thank you in advance for your help!

 

Related to

• Wrong Result

0

• 

  Simranjit Kaur

  Gurobi Staff

  • May 06, 2024 00:34

  Hi Marith,

  How are you getting the below values?

  - Fixed costs: 500000
  - Additional capacity costs: 7770.0
  - Operational costs: 155400.0
  - Charging costs: 171.05
  - Total costs: 663341.05
  - Total revenue: 280383.04

  Once the model is solved, could you please query the X attribute of the revenue variable (or variables that make up revenue) and the total_cost variable (or variables that make up total_cost)? Their difference should match the objective value.

  Best regards,
  Simran

  0

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