Forum Discussion
Using callback to re-set (modify) control in middle on B&B search [Using Python]
Hello Xpress Experts,
I am wondering if any of you could help me with this callback in Python. I want to quickly find an integer solution during the BB, and then, switch to the default BB search settings of Xpress.
To do that, I am trying to set a callback such that after the first integer solution is found, the setControl for SBBEST and SBESTIMATE are re-set. Also, I do not want to keep using such callback function further in the BB, so I want to remove it.
Below you can see a piece of the code where I am trying to achieve what I mentioned before. Can anyone tell me why Xpress is stopping immediately after the first integer solution is found and says that stopped by user?
# Define callback to depth search first and then switch to Xpress default
def change_search_strategy(prob):
prob.setControl({'sbbest':-1,'sbestimate':-1})
print("CHANGED THE BRANCH STRATEGY")
prob.removecbintsol()
# Add function to callback
p.addcbintsol(change_search_strategy, None,0)
2 Replies
Not an answer to your question but would it not be much simpler to
- Set your special parameters
- Set the integer solution limit (MAXMIPSOL) to 1
- Call solve()
- Reset your special parameters and reset the integer solution limit to its default.
- Call solve()
This should give you the same effect but without any callbacks.
Hi Daniel,
First of all, thanks a lot for your message. Actually, I ended up doing something like that, I interrupted the search and reset the parameters. But MaxMipsol seems to do exactly the same but effortless. I am just getting to know all the capabilities, so I missed that control parameter.
Thanks a lot, it is really helpful.
