What does AttributeError: 'LpElement' object has no attribute 'cat' and why is this error produced?

Question

我正在尝试使用 Python PuLP

对以下方程建模

我写了下面的Python代码

prob = LpProblem('Resource', LpMaximize)

# x variables

xs = [LpVariable("x{0}{1}{2}".format(i + 1, j + 1, k + 1), cat = "Binary")

    for i in range(0, 3)
    for j in range(0, 5)
    for k in range(0, 2)
]

print("\nX Variable\n")

for i in range(0, len(xs)):
    print(xs[i])

# y variables

ys = [LpVariable("y{0}{1}".format(i + 1, j + 1), cat = "Binary")

    for i in range(0, 3)
    for j in range(0, 5)
]

print("\nY Variable\n")
for i in range(0, len(ys)):
    print(ys[i])


for j in range(0, 5):
    for k in range(0, 2):
    for i in range(0, 3):
    con = "x{0}{1}{2} <= y{3}{4}".format(i + 1, j + 1, k + 1, i + 1, j + 1)
prob += LpAffineExpression(LpElement(con))
print(con)

status = prob.solve()

这会产生以下 PuLP 错误：

Traceback (most recent call last): File "C:\Python34\Cloud 3.py", line 446, in resource(request, pmachine, l, q) File "C:\Python34\Cloud 3.py", line 136, in resource status = prob.solve() File "C:\Python34\lib\site-packages\pulp-1.6.1-py3.4.egg\pulp\pulp.py", line 1643, in solve status = solver.actualSolve(self, **kwargs) File "C:\Python34\lib\site-packages\pulp-1.6.1-py3.4.egg\pulp\solvers.py", line 1303, in actualSolve return self.solve_CBC(lp, **kwargs) File "C:\Python34\lib\site-packages\pulp-1.6.1-py3.4.egg\pulp\solvers.py", line 1325, in solve_CBC tmpMps, rename = 1) File "C:\Python34\lib\site-packages\pulp-1.6.1-py3.4.egg\pulp\pulp.py", line 1431, in writeMPS if mip and v.cat == LpInteger: AttributeError: 'LpElement' object has no attribute 'cat'

AttributeError: 'LpElement' object has no attribute 'cat' 是什么意思，为什么会产生这个错误？

Answer 1

当问题变量（在本例中为 prob = LpProblem('Resource', LpMaximize) 与添加的约束不兼容时，会产生 AttributeError: 'LpElement' object has no attribute 'cat'。

当使用指定的 PuLP LpVariable.dicts 而不是像上面那样动态生成变量来定义变量时，可以通过删除冗余 LpAffineExpression(LpElement(con)) 调用来解决此问题。

合并更改的更好方法如下：

prob = LpProblem('Resource', LpMaximize)

xdict = LpVariable.dicts('', ["x{0}{1}{2}".format(i + 1, j + 1, k + 1)
        for i in range(0, len(request))
        for j in range(0, len(pmachine))
        for k in range(0, pmachine[j].npj)
    ],
    0, 1, cat = 'Binary')

ydict = LpVariable.dicts('', ["y{0}{1}".format(i + 1, j + 1)
        for i in range(0, len(request))
        for j in range(0, len(pmachine))
    ],
    0, 1, cat = 'Binary')

for i in range(0, len(request)):
    for j in range(0, len(pmachine)):
        for k in range(0, pmachine[j].npj):
            con = xdict["x{0}{1}{2}".format(i + 1, j + 1, k + 1)] <= ydict["y{0}{1}".format(i + 1, j + 1)]
            prob += con
            print(con)

What does AttributeError: 'LpElement' object has no attribute 'cat' and why is this error produced?

What does AttributeError: 'LpElement' object has no attribute 'cat' and why is this error produced?

python

mathematical-optimization

linear-programming

pulp