Pyomo:从Python代码访问解决方案 [英] Pyomo: Access Solution From Python Code

问题描述

我有一个线性整数程序要解决.我安装了求解器glpk(感谢此答案)和pyomo.我写了这样的代码:

I have a linear integer programme I want to solve. I installed solver glpk (thanks to this answer) and pyomo. I wrote code like this:

from pyomo.environ import *
from pyomo.opt import SolverFactory

a = 370
b = 420
c = 2

model             = ConcreteModel()
model.x           = Var([1,2], domain=NonNegativeIntegers)
model.Objective   = Objective(expr = a * model.x[1] + b * model.x[2], sense=minimize)
model.Constraint1 = Constraint(expr = model.x[1] + model.x[2] == c)
# ... more constraints

opt = SolverFactory('glpk')

results = opt.solve(model)

这将产生文件results.yaml的解决方案.

This produces solution to file results.yaml.

我要使用相同的模型解决许多问题，但使用不同的a，b和c值.我想为a，b和c分配不同的值，求解模型，获得model.x[1]和model.x[2]的解决方案，并列出a，b，，model.x[1]和model.x[2].我阅读了文档，但是示例仅将解决方案写入文件，例如results.yaml.

I have many problems I want to solve using the same model but with different a, b, and c values. I want to assign different values to a, b, and c, solve the model, obtain solution of model.x[1] and model.x[2], and have a listing of a, b, c, model.x[1] and model.x[2]. I read documentation but examples only write solutions to file such as results.yaml.

我可以通过任何方式访问代码中的解决方案值吗?

Is there any way I can access to solution values from code?

谢谢

推荐答案

我不确定这是否是您要寻找的东西，但这是在某些脚本中打印一些变量的一种方式.

I'm not sure if this is what you are looking for, but this is a way that I have some variables being printed in one of my scripts.

from pyomo.environ import *
from pyomo.opt import SolverFactory
from pyomo.core import Var

M = AbstractModel()
opt = SolverFactory('glpk')

# Vars, Params, Objective, Constraints....

instance = M.create_instance('input.dat') # reading in a datafile
results = opt.solve(instance, tee=True)
results.write()
instance.solutions.load_from(results)

for v in instance.component_objects(Var, active=True):
    print ("Variable",v)
    varobject = getattr(instance, str(v))
    for index in varobject:
        print ("   ",index, varobject[index].value)

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