Forum Discussion
Are preintsol callbacks threadsafe?
The optimizer documentation states "When the MIP callbacks are called they are MUTEX protected to allow non threadsafe user callbacks." In my Java code for one-tree Benders, if I specify a single thr...
I agree that the toString() function should work. Unfortunately, at the moment it does not and at the moment this is the expected behavior (for the technical reasons described above). I have filed an internal request for improvement. Obviously, printing out a cut for debugging reasons is a very valid use case that should work out of the box.
You get this NullPointerException from XpressProblem.getVariables() because the problem passed into the callback is in presolved state and thus has no Variable instances: interaction with a model in presolved state requires indices rather than Variable instances to reference columns.
So everything boils down to the known limitation that LinExpression.toString() does not work from inside a callback.
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How to make cuts added in a preIntsol callback globally valid (root node) instead of local to the current subtree?
I'm using the Xpress Optimizer Java API (com.dashoptimization, Xpress 9.4) to solve a MIP with lazy constraints that are generated dynamically. My constraints are all globally valid — they are not lo...