How to print out "root node" information when solving a MIP with Gurobi?
Ongoing
I need to print out root node time/gap/bounds when solving a MIP with Gurobi. Is there any built-in attribute that we can call to print out these values? I am using Python as the main programming language.
The parameters I am looking for are very similar to the ones shown in Table 1 of the following Management Science paper by Fischetti et al. (2016) by the title of "Redesigning Benders Decomposition for Large-Scale Facility Location".
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Hi Ali,
There is no attribute to directly query the root relaxation value. There are several other alternatives:
- Gurobi log file includes a message like below at the end of root node solve where you can find the root relaxation value.
Root relaxation: objective 1.415000e+03, 85 iterations, 0.00 seconds (0.00 work units)- You can use Gurobi callbacks (either the MIPNODE or the MESSAGE callback) to obtain the value of the root relaxation programmatically.
- In the MIPNODE callback, the first queried MIPNODE_OBJBND value will give the root relaxation with no cutting planes when MIPNODE_NODCNT equals 0.
- See the example callback.py on how to use callbacks in Gurobi Python API.
- You can use the GRBlogtools open-source Python package which parses the Gurobi log and saves it in a pandas DataFrame. You can then find the root relaxation value in a column named \(\texttt{RelaxObj}\).
Best regards,
Maliheh
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Hi Maliheh,
Thank you for the detailed response. This is indeed helpful.
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Hi,
I have two related questions.
- Should I expect the first queried MIPNODE_OBJBND (when MIPNODE_NODCNT equals 0) to be equal to the plain LP relaxation?
- Is it correct to assume that the last queried MIPNODE_OBJBND (when MIPNODE_NODCNT equals 0) corresponds to the value of the relaxed problem after the last added cut (right before branching)?
Best,
Felipe
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