Can we print constraints as they are added? Hows?

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D

2023年05月02日 23:36

Trying to track why is the script taking too long, Anyone knows if we can print values while the model is building constructed.

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Maliheh Aramon

Gurobi Staff

2023年05月03日 01:06
Are you using a third-party API or a Gurobi API to build your model? Please have a look at the strategies outlined in the article "How do I improve the time to build my model?" to first identify the bottlenecks in your script and then make modifications accordingly.

The response to your question in the title of the post is yes. The model modifications are performed in a lazy fashion in the Gurobi Optimizer. Therefore, in order to query constraints' attributes (for sanity checks) before the model is optimized, you would need to call the model.update() method explicitly. See the script below as an example.
```
# Add the constraint \sum x_i <= 10
model.addConstr(x.sum() <= 10, name="c0")
# Add the constraint c to the model
model.update()
# Query the LHS, the RHS, and the sense of the constraint c0
c0 = model.getConstrByName("c0")
LHS, RHS, sense = model.getRow(c0), c0.RHS, c0.Sense
```
Printing \(\texttt{LHS}\), \(\texttt{RHS}\), and \(\texttt{sense}\) should give:
```
In [16]: LHS
Out[16]: <gurobi.LinExpr: x[0] + x[1] + x[2] + x[3] + x[4] + x[5] + x[6] + x[7] + x[8] + x[9]>

In [17]: RHS
Out[17]: 10.0

In [18]: sense
Out[18]: '<'
```
The article "How do I access the left-hand side of a constraint?" is also a useful read.

Best regards,

Maliheh
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