AttributeError是什麼：'LpElement'對象沒有屬性'cat'，爲什麼會產生這個錯誤？

Question

我試圖用Python紙漿下列公式

我寫了下面的Python代碼

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() 

這給跟隨漿誤差模型：

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'是什麼以及爲什麼產生這個錯誤？

Answer 1

AttributeError: 'LpElement' object has no attribute 'cat'是在問題變量（本例中爲prob = LpProblem('Resource', LpMaximize)）與約束被添加之間存在不兼容問題時產生的。

這可以通過刪除多餘的LpAffineExpression(LpElement(con))調用來解決，當變量使用指定的LpVariable.dicts指定的PuLP定義時，而不是像上面所做的那樣動態生成變量。

結合變化的更好的辦法如下：

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)