问题描述
我有一个模型,需要向其添加新约束,但是我希望尽可能地“仅”实施此规则。有没有办法用cplex或docplex来实现呢?
解决方法
您可以使用松弛来使约束变软:
from docplex.mp.model import Model
mdl = Model(name='buses')
nbbus40 = mdl.integer_var(name='nbBus40')
nbbus30 = mdl.integer_var(name='nbBus30')
slack=mdl.integer_var(name='slack')
mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 300,'kids')
mdl.add_constraint(nbbus40+nbbus30<=7+slack,'softconstraint')
mdl.minimize(nbbus40*500 + nbbus30*400+10000*slack)
mdl.solve()
mdl.export("c:\\temp\\buses.lp")
for v in mdl.iter_integer_vars():
print(v," = ",v.solution_value)
给出
nbBus40 = 6.0
nbBus30 = 2.0
slack = 1.0
为什么不尝试逻辑约束呢?
https://github.com/AlexFleischerParis/zoodocplex/blob/master/zooifthen.py
from docplex.mp.model import Model
mdl = Model(name='buses')
nbbus40 = mdl.integer_var(name='nbBus40')
nbbus30 = mdl.integer_var(name='nbBus30')
mdl.add_constraint(nbbus40*40 + nbbus30*30 >= 300,'kids')
mdl.minimize(nbbus40*500 + nbbus30*400)
mdl.solve()
for v in mdl.iter_integer_vars():
print(v,v.solution_value)
print()
print("with if nb buses 40 more than 3 then nbBuses30 more than 7")
#if then constraint
mdl.add(mdl.if_then(nbbus40>=3,nbbus30>=7))
mdl.minimize(nbbus40*500 + nbbus30*400)
mdl.solve()
for v in mdl.iter_integer_vars():
print(v,v.solution_value)
'''
which gives
nbBus40 = 6.0
nbBus30 = 2.0
with if nb buses 40 more than 3 then nbBuses30 more than 7
nbBus40 = 0
nbBus30 = 10.0
'''