Weird behavior in simple problem

[markjreed]

Tried to implement the municipal department numbers problem. Obviously this is a trivial problem that is amenable to a brute-force solution, but I thought it would be a good toy exercise for the constraint solver. However, I'm getting inconsistent results from run to run; it only produces the correct result about half the time, so I wonder if I'm doing something incorrectly.

This is my attempt:

use ProblemSolver;

my ProblemSolver $p .= new;
my @vars = «police sanitation fire»;
for @vars -> $dept {
  $p.add-variable($dept, 1..7);
}
$p.unique-vars(@vars);
$p.add-constraint: -> :$police! { $police %% 2 };
$p.add-constraint: -> :$police!, :$sanitation!, :$fire! { $police + $sanitation + $fire == 12 };

.say for $p.solve;

One run will output the correct 14 solutions, while the next will include 16 additional solutions in which the value for police is odd, ignoring the middle constraint above.

[FCO]

Thanks for your message. Sorry for taking so long to respond. I’ll take a look at it as soon as possible, when I’m back home from vacation. Thanks