[英]Why doesn't Choco-solver find a solution?
I'm learning to use Choco-solver .我正在学习使用Choco-solver 。 I found that it fails to find a solution to a very simple problem, which means that I must have misunderstood something...
我发现它无法找到一个非常简单的问题的解决方案,这意味着我一定误解了一些东西......
I reduced my code to this:我将我的代码简化为:
Model model = new Model("Minimum");
IntVar x = model.intVar("x", 1, 9, false);
IntVar y = model.intVar("y", 1, 9, false);
IntVar z = model.intVar("z", -1000, 1000, false);
z.eq(x.add(y.mul(2))).post();
Solver solver = model.getSolver();
solver.showStatistics();
solver.showSolutions();
solver.findSolution();
So, three integer variables and one constraint saying that z = x + 2y
.因此,三个 integer 变量和一个约束说
z = x + 2y
。 Choco-solver responds Complete search - No solution
. Choco-solver 响应
Complete search - No solution
。
I find that I get correct solutions if I change the inner part of the constraint from y.mul(2)
to y.mul(1)
(x = 1, y = 1, z = 2) or to y.add(2)
(x = 1, y = 1, z = 4).如果我将约束的内部部分从
y.mul(2)
更改为y.mul(1)
(x = 1, y = 1, z = 2) 或y.add(2)
2),我发现我得到了正确的解决方案y.add(2)
(x = 1, y = 1, z = 4)。 I can even set it to y.mul(-2)
(x = 1 y = 9 z = -17), but if I use mul
with an integer larger than 1 the constraint seems to be unsolveable.我什至可以将其设置为
y.mul(-2)
(x = 1 y = 9 z = -17),但如果我使用mul
的 integer 大于 1,则约束似乎无法解决。
What is going on here?这里发生了什么?
This was indeed a bug in Choco Solver 4.10.7.这确实是 Choco Solver 4.10.7 中的一个错误。 This bug has been fixed since: https://github.com/chocoteam/choco-solver/issues/841
此错误已得到修复: https://github.com/chocoteam/choco-solver/issues/841
If you want to use the fixed version, I invite you to download the code from GitHub and compile it using Maven.如果您想使用固定版本,我邀请您从 GitHub 下载代码并使用 Maven 进行编译。
Concerning your constraint, I advise you to post an arithm constraint as following: model.arithm(x, "+", y.mul(2).intVar(), "=", z).post();
关于你的约束,我建议你发布一个算术约束如下:
model.arithm(x, "+", y.mul(2).intVar(), "=", z).post();
. . This way, you avoid having an intermediate variable corresponding to "x+2*y" that you force to be equal to z.
这样,您就避免了一个与“x+2*y”相对应的中间变量,您强制它等于 z。 It does not really matter in such a small example, but it could lead to memory issues on bigger problems while relying on ArExpression (for Arithmetical Expression).
在这样一个小例子中并不重要,但它可能导致 memory 在依赖 ArExpression(用于算术表达式)时出现更大的问题。
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