fzn2smt solver answers with `unknown` on tested formulas

Question

The fzn2smt tool allows one to solve flatzinc formulas via Yices.

When I try to run it, the solver answers with UNKNOWN to every formula I test. e.g.:

~$ java -Xmx4096M fzn2smt -ce "./yices-2.5.2/bin/yices -f" -i 2DPacking.fzn 
Time1:170
=====UNKNOWN=====

However, on the given example, it seems to correctly create the 2DPacking.fzn.smt instance in the same directory of the 2DPacking.fzn file:

~$ ls
2DPacking.fzn.smt    2DPacking.fzn    2DPacking.mzn    2DPacking.ozn

If I manually run Yices over the smt formula, I get a positive result:

~$ yices-smt -f 2DPacking.fzn.smt 
sat

(= x____00002_6_ 0)
...

IMPLICANT:
(>= x____00003_4_ 0)
...

Q: Does anyone else have experience with fzn2smt and know how to fix this issue?

Just to be sure that the issue I am experiencing is not due to the installation part, I will share it here:

 main_dir
 main_dir/fzn2smt-2-0-02      # unpacked fzn2smt files
 main_dir/antlr               # unpacked antlr-runtime-3.5 files
 main_dir/yices-2.5.2         # unpacked yices files

I also modified the environment variables as requested by the tool instructions:

 PATH=${main_dir}/yices-2.5.2/bin/:${PATH}
 PATH=${main_dir}/fzn2smt-2-0-02/:${PATH}

 CLASSPATH=${main_dir}:${CLASSPATH}
 CLASSPATH=${main_dir}/antlr:${CLASSPATH}
 CLASSPATH=${main_dir}/fzn2smt-2-0-02:${CLASSPATH}

`fzn2smt` is a rather old tool, while you're using the newest version of Yices. This might just be unexpected output from Yices that `fzn2smt` doesn't yet understand. I know this won't help with your problem, but I'm afraid it is a bug in `fzn2smt`. — Dekker1, Sep 19 '17 at 23:30

Patrick Trentin · Accepted Answer · 2017-09-20T10:59:57.833

As @Dekker suggested in the comments, the issue is due to fzn2smt seemingly not being updated in a while.

After some trials and errors, I found out that the most recent version of Yices that appears to be compatible with fzn2smt is version 2.2.1.

It can be executed as follows:

~$ java -Xmx4096M fzn2smt -ce "./yices-2.2.1/bin/yices-smt -f" -i 2DPacking.fzn
Time1:162
Time: 207
Pos: 0
item = array2d(1..2, 1..4, [0, 0, 0, 0, 1, 1, 1, 1]);
obj = 1;
----------
Time: 223
Pos: 0
item = array2d(1..2, 1..4, [0, 0, 0, 0, 1, 1, 1, 1]);
obj = 1;
----------
==========
Time2:228

Originally, fzn2smt was coupled with version 2 of Yices presented at the SMT-COMP 2009. To use that version, the command-line instruction to use the tool is slightly different:

~$ java -Xmx4096M fzn2smt -ce "./yices2smt09/bin/yices -f" -i 2DPacking.fzn
Time1:160
Time: 208
Pos: 0
item = array2d(1..2, 1..4, [0, 0, 0, 0, 1, 1, 1, 1]);
obj = 1;
----------
==========
Time2:223

Notice that

the executable is named yices here, rather than yices-smt
the output is slightly different, for some reasons the solution is printed more than once when using the newer version of the tool

Old versions of Yices can be downloaded from here.

fzn2smt solver answers with `unknown` on tested formulas

1 Answers1