old vs new version of Z3

Question

I have an instance which could be very efficiently solved by old version of Z3(version 2.18). It return SAT in a few seconds. However, when I try it on the current version of Z3(version 4.3.1). It does not return any result after 10 minutes.

Here are some details about the experiment. Could anybody give some advice?

• there are 4000 Bool variables and 200 Int variables

• all the constraint are in propositional logic with comparison between integers like a < b

• platform: open suse linux 12.3@thinkpad T400s

• Z3 v2.18 was downloaded as a linux binary last year (I cannot find the link now)

• Z3 v4.3.1 was downloaded as source code, and I compile it on my laptop by using the default setting

There are about 50,000 lines in the smt file, so I can not post it here. I would be happy to send the file by email if anybody are interested. Thanks.

Answer 1

Z3 is a portfolio of solvers. The default configuration changes from version to version. Progress is never monotonic. That is, a new version may solve more problems, but may be slower and fail in some problems.

Remark: the author has sent his benchmark by email to the Z3 authors.

In the “work-in-progress” branch, I managed to reproduce the Z3 2.19 performance by using

            (set-option :smt.auto-config false)

Here are instructions on how to download the “work-in-progress” branch.

To get the same behavior, we also have to replace (check-sat) with (check-sat-using smt)

BTW, in the official release, we have to use

            (set-option :auto-config false)

instead of

            (set-option :smt.auto-config false)