Python中的PuLP找不到最大值

Question

I've been using the code below for some time now and it's always been able to find the max/min except for now.

I get one corner point to this: x=168, y=192, objective=3288

But there is a corner point that is the true max: x=0, y=304, objective=3344

What am I doing wrong that makes this code unable to find the x,y that truly maximizes the objective?

from pulp import LpVariable, LpProblem, LpMaximize, LpStatus, value, LpMinimize

# declare your variables
x = LpVariable("y1", 0, None)
y = LpVariable("y2", 0, None)

# defines the problem
prob = LpProblem("problem", LpMaximize)

# defines the constraints
prob += 1/2*x+3/4*y == 228
prob += 1/2*x+1/4*y == 132

# defines the objective function to maximize
prob += 7*x+11*y

# solve the problem
status = prob.solve()
LpStatus[status]
# print the results
print('x={0},y={1}.'.format(round(value(x)),round(value(y))))
print("The objective is ${}.".format(round(value(prob.objective))))

Answer 1

Consider the constraint prob += 1/2*x+1/4*y == 132 .
If you set x=0 and y=304 this constraint would be violated ( 76 ≠ 132).
To test a solution you can just add the constraints:

prob+= x == 0
prob+= y == 304

status = prob.solve()
print(LpStatus[status])

which outputs Infeasible .