我正在研究Pyomo优化脚本 . 它具有索引参数和变量以及8个约束的中等复杂性 . 如果我将决策变量保留为没有初始值，那么对于涉及决策变量的约束，我会得到“错误：评估表达式：未初始化的NumericValue对象没有值”错误 . 如果我将决策变量初始化为1或0，则求解器（glpk）返回状态：最佳和目标函数值= 0.所有决策变量也设置为0.我正在寻找有关如何解决此问题的想法 . 下面是相关代码（没有数据）以及解算器和model.display的输出，它们已被编辑以使其更紧凑 .
#Sets
#clinics
model.C = Set(initialize=list(clinics.keys()))
#clients
model.B = Set(initialize=list(client_blocks.keys()))
#scalar params
model.clt_stf_max = 10
model.tt_max = 45
model.selected_clinic_max = 4
model.stf_max = sum(staff_cap.values()) #total available staff is sum of clinic new staff capacity
model.z_M = 5000 #used in clients at selected clinics constraint
model.e_M = 500 #used in staff at selected clinics constraint
#indexed params
model.cnc_stf_cap = Param(C, initialize=staff_cap)
model.clt_blk = Param(B, initialize=client_blocks)
model.trav_time = Param(T, initialize=trav_time)
#decision vars
#x new staff at each clinic
model.new_stf = Var(model.C, domain=NonNegativeIntegers, initialize=0)
#y new clients at each clinic/block combo
model.new_clt = Var(model.C, model.B, domain=NonNegativeIntegers, initialize=0)
#z client at selected clinics only
model.z = Var(model.C, model.B, domain=Binary, initialize=0)
#e staff at selected clinics only
model.e = Var(model.C, domain=Binary, initialize=0)
#objective function
def o_min_tt_rule(model):
return sum(model.trav_time[c,b]*model.new_clt[c,b] for c in model.C for b in model.B)
model.o_min_tt = Objective(rule=o_min_tt_rule, sense=minimize)
#constraints
# limit new clients at clinic to staff capacity
def limit_clients_to_clinic_staff_cap_rule(model, c):
return sum(model.new_clt[c,b] for c in model.C for b in model.B) <= (model.cnc_stf_cap[c] * model.clt_stf_max)
model.limit_clients_to_clinic_staff_cap = Constraint(model.C, rule=limit_clients_to_clinic_staff_cap_rule)
#total of new clients served in block should not exceed the number new clients in the block
def limit_newclient_block_rule(model, b):
return sum(model.new_clt[c,b] for c in model.C for b in model.B) <= (model.clt_blk[b])
model.limit_newclient_block = Constraint(model.B, rule=limit_newclient_block_rule)
#limit new clients to selected clinics
def client_to_selected_clinic_rule(model, c, b):
return model.new_clt[c,b] <= model.z[c,b] * model.z_M
model.client_to_selected_clinic = Constraint(model.C, model.B, rule=client_to_selected_clinic_rule)
#limit single client travel time to max travel time minutes
def limit_client_travtime_rule(model, c, b):
return (model.trav_time[c,b] * model.z[c,b]) <= model.tt_max
model.limit_client_travtime = Constraint(model.C, model.B, rule=limit_client_travtime_rule)
#limit selected clinics to max number
def limit_selected_clinic_to_max_rule(model):
return summation(model.e) <= model.selected_clinic_max
model.limit_selected_clinic_to_max = Constraint(rule=limit_selected_clinic_to_max_rule,)
#limit new staff to selected clinics
def staff_to_selected_clinic_rule(model, c):
return model.new_stf[c] <= model.e[c] * model.e_M
model.staff_to_selected_clinic = Constraint(model.C, rule=staff_to_selected_clinic_rule)
#limit new staff at clinic to clinic capacity
def limit_staff_to_clnic_cap_rule(model, c):
return model.new_stf[c] <= model.cnc_stf_cap[c]
model.limit_staff_to_clnic_cap = Constraint(model.C, rule=limit_staff_to_clnic_cap_rule)
#limit total new staff to staff max
def limit_tot_staff_rule(model):
return summation(model.new_stf) <= model.stf_max
model.limit_tot_staff = Constraint(rule=limit_tot_staff_rule)
# solve the model
solver = SolverFactory("glpk", tee=True, warmstart=True, symbolic_solver_labels=True)
从求解器和model.display（）输出
SOLVER:
Problem:
- Name: unknown
Lower bound: 0.0
Upper bound: 0.0
Number of objectives: 1
Number of constraints: 753
Number of variables: 665
Number of nonzeros: 29213
Sense: minimize
Solver:
- Status: ok
Termination condition: optimal
Statistics:
Branch and bound:
Number of bounded subproblems: 1
Number of created subproblems: 1
Error rc: 0
Time: 0.10507559776306152
Solution:
- number of solutions: 1
number of solutions displayed: 1
- Gap: 0.0
Status: optimal
Message: None
Objective:
o_min_tt:
Value: 0
Variable: No nonzero values
Constraint: No values
模型：
Model (Staff_Allocation)
Variables:
new_stf : Size=4, Index=Clinics
Key : Lower : Value : Upper : Fixed : Stale : Domain
FEDCAP Counseling Center - 01004 : 0 : 0 : None : False : False : NonNegativeIntegers
The Salvation Army Belmont Center - 04002 : 0 : 0 : None : False : False : NonNegativeIntegers
VIP Wellness Center - 12000 : 0 : 0 : None : False : False : NonNegativeIntegers
Westchester Center of Excellence - 11006 : 0 : 0 : None : False : False : NonNegativeIntegers
new_clt : Size=392, Index=new_clt_index
Key : Lower : Value : Upper : Fixed : Stale : Domain
('FEDCAP Counseling Center - 01004', 360050019001022) : 0 : 0 : None : False : False : NonNegativeIntegers
z : Size=392, Index=z_index
Key : Lower : Value : Upper : Fixed : Stale : Domain
('FEDCAP Counseling Center - 01004', 360050019001022) : 0 : 0 : 1 : False : False : Binary
e : Size=4, Index=Clinics
Key : Lower : Value : Upper : Fixed : Stale : Domain
FEDCAP Counseling Center - 01004 : 0 : 0 : 1 : False : False : Binary
The Salvation Army Belmont Center - 04002 : 0 : 0 : 1 : False : False : Binary
VIP Wellness Center - 12000 : 0 : 0 : 1 : False : False : Binary
Westchester Center of Excellence - 11006 : 0 : 0 : 1 : False : False : Binary
Objectives:
o_min_tt : Size=1, Index=None, Active=True
Key : Active : Value
None : True : 0
Constraints:
limit_clients_to_clinic_staff_cap : Size=4
Key : Lower : Body : Upper
FEDCAP Counseling Center - 01004 : None : 0 : 200.0
The Salvation Army Belmont Center - 04002 : None : 0 : 150.0
VIP Wellness Center - 12000 : None : 0 : 150.0
Westchester Center of Excellence - 11006 : None : 0 : 250.0
limit_newclient_block : Size=98
Key : Lower : Body : Upper
360050019001022 : None : 0 : 1.0
.... 97 more like this
client_to_selected_clinic : Size=392
Key : Lower : Body : Upper
('FEDCAP Counseling Center - 01004', 360050019001022) : None : 0 : 0.0
.... 391 more like this
limit_client_travtime : Size=392
Key : Lower : Body : Upper
('FEDCAP Counseling Center - 01004', 360050019001022) : None : 0 : 75.0
.... 391 more like this
limit_selected_clinic_to_max : Size=1
Key : Lower : Body : Upper
None : None : 0 : 4.0
staff_to_selected_clinic : Size=4
Key : Lower : Body : Upper
FEDCAP Counseling Center - 01004 : None : 0 : 0.0
The Salvation Army Belmont Center - 04002 : None : 0 : 0.0
VIP Wellness Center - 12000 : None : 0 : 0.0
Westchester Center of Excellence - 11006 : None : 0 : 0.0
limit_staff_to_clnic_cap : Size=4
Key : Lower : Body : Upper
FEDCAP Counseling Center - 01004 : None : 0 : 4.0
The Salvation Army Belmont Center - 04002 : None : 0 : 3.0
VIP Wellness Center - 12000 : None : 0 : 3.0
Westchester Center of Excellence - 11006 : None : 0 : 5.0
limit_tot_staff : Size=1
Key : Lower : Body : Upper
None : None : 0 : 15.0