Z3 randomness of generated model values

Question

I\'m trying to influence the randomness of results for model values generated by Z3. As far as I understand, the options for this are very limited: in case of linear arithmetic,

Answer 1

Thanks for catching that! There was indeed a bug that caused the random seed not to be passed through to the arithmetic theory. This is now fixed in the unstable branch (fix here).

This example:

(set-option :smt.arith.random_initial_value true)
(declare-const x Int)
(declare-const y Int)
(assert (> (+ x y) 0))
(check-sat-using (using-params qflra :random_seed 1))
(get-model)
(check-sat-using (using-params qflra :random_seed 2))
(get-model)
(check-sat-using (using-params qflra :random_seed 3))
(get-model)

Now produces three different models:

sat
model
  (define-fun y () Int
    4294966763)
  (define-fun x () Int
    4294966337)
)
sat
(model
  (define-fun y () Int
    216)
  (define-fun x () Int
    4294966341)
)
sat
(model
  (define-fun y () Int
    196)
  (define-fun x () Int
    4294966344)
)

It looks like there may be another place where this option isn't passed through correctly (e.g., when using set-logic instead of calling the qflra tactic directly), we're still looking into that.