z3 minimization and timeout

Question

I try to use the z3 solver for a minimization problem. I was trying to get a timeout, and return the best solution so far. I use the python API, and the timeout option \"smt

Answer 1

Z3 finds solutions for the hard constraints and records the current values for the objectives and soft constraints. The last model that was found (the last model with the so-far best value for the objectives) is returned if you ask for a model. The maxres strategy mainly improves the lower bounds on the soft constraints (e.g., any solution must have cost at least xx) and whenever possible improves the upper bound (the optional solution has cost at most yy). The lower bounds don't tell you too much other than narrowing the range of possible optimal values. The upper bounds are available when you timeout. You could try one of the other strategies, such as the one called "wmax", which performs a branch-and-prune. Typically maxres does significantly better, but you may have better experience (depending on the problems) with wmax for improving upper bounds.

I don't have a mode where you get a stream of models. It is in principle possible, but it would require some (non-trivial) reorganization. For Pareto fronts you make successive invocations to Optimize.check() to get the successive fronts.