python 中的 xpress 库使用 addConstraint 时约束无效

Question

当运行这段代码

import numpy as np
import xpress as xp

z = np.array([xp.var () for i in range (200)]).reshape (4,5,10)
t = np.array([xp.var (vartype = xp.binary) for i in range (200)]).reshape (4,5,10)
p = xp.problem()
p.addVariable(z,t)
p.addConstraint(z <= 1 + t)

我收到以下错误

Invalid constraint
---------------------------------------------------------------------------
ModelError                                Traceback (most recent call last)
      3 p = xp.problem()
      4 p.addVariable(z,t)
----> 5 p.addConstraint(z <= 1 + t)
      6 p.addConstraint(xp.Sum(z[i][j][k] for i in range (4) for j in range (5)) <= 4 for k in range (10))
ModelError: Invalid constraint

任何帮助将不胜感激，因为我不确定如何修复它！

Answer 1

np 数组的 dtype 必须显式设置为 xp.npvar。这表示 here:

The NumPy arrays must have the attribute dtype equal to xpress.npvar (abbreviated to xp.npvar here) in order to use the matricial/vectorial form of the comparison (<=, =, >=), arithmetic (+, -, *, /, **), and logic (&, |) operators.

如果您不将类型设置为 npvar，将使用这些运算符的错误重载，并且 z <= 1 - t 将只是一个布尔数组。

这是创建数组的正确方法：

z = np.array([xp.var () for i in range (200)], dtype=xp.npvar).reshape (4,5,10)
t = np.array([xp.var (vartype = xp.binary) for i in range (200)], dtype=xp.npvar).reshape (4,5,10)

python 中的 xpress 库使用 addConstraint 时约束无效

Invalid Constraint when using the addConstraint with the xpress library in python

python

numpy

binary

solver

xpress-optimizer