Jupyter Python 上的 MiniZinc

问题描述

我正在尝试在 Jupyter 中使用 Minizinc。我已经安装了所有的包，但是当我运行模型时，它运行了一个错误。我尝试使用 MiniZinc Python pdf 上的示例，但它运行相同的错误。代码是：

from minizinc import Instance,Model,Solver

gecode = Solver.lookup("gecode")

model = Model()
model.add_string(
    """
    include "all_different.mzn";
    set of int: A;
    set of int: B;
    array[A] of var B: arr;
    var set of B: X;
    var set of B: Y;

    constraint all_different(arr);
    constraint forall (i in index_set(arr)) ( arr[i] in X );
    constraint forall (i in index_set(arr)) ( (arr[i] mod 2 = 0) <-> arr[i] in Y );
    """
)

instance = Instance(gecode,model)
instance["A"] = range(3,8)  # MiniZinc: 3..8
instance["B"] = {4,3,2,1,0}  # MiniZinc: {4,0}

result = instance.solve()
print(result["X"])  # range(0,5)
assert isinstance(result["X"],range)
print(result["Y"])  # {0,4}
assert isinstance(result["Y"],set)

然后 Jupyther 返回：

RuntimeError: asyncio.run() cannot be called from a running event loop

解决方法

按照安装步骤操作，正如他们所说，这很神奇！ Using MiniZinc in Jupyter Notebooks。

只需运行 pip install -U iminizinc，然后您的单元格将如下所示：

%load_ext iminizinc

(^ 这可能会导致白色输出和奇怪的青色错误，以防万一，忽略它。如果你想确保你成功加载了 minizinc，再次运行单元格，像 The iminizinc extension is already loaded.应该出现）

# regular python assigments.
# Note that set and range are not JSON serializable,you will need
# always to convert your iterables to list

A = list(range(3,8))
B = [4,3,2,1,0]

%%minizinc

include "all_different.mzn";
set of int: A;
set of int: B;
array[A] of var B: arr;
var set of B: X;
var set of B: Y;

constraint all_different(arr);
constraint forall (i in index_set(arr)) ( arr[i] in X );
constraint forall (i in index_set(arr))
    ( (arr[i] mod 2 = 0) <-> arr[i] in Y );

最后一个单元格实际上是 minizinc 代码，在单元格内执行，输出将是您的解决方案。

如果您正在寻找所有可能的解决方案，只需将标志 -a 添加到魔法中：%%minizinc -a

您还可以使用标志 -m bind: %%minizinc -m bind 将输出绑定到 python 变量。在您的情况下，您可以在另一个单元格中检查您的输出变量，如下所示：

arr # => [0,4]

要获得所有可用的标志，请使用魔法：%%minizinc?

minizinc python python-asyncio runtime runtime runtime