Unable to retrieve attribute 'objVal'

回答済み

Dhiraj Yadav

2024年05月16日 12:38

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import gurobipy as gp
from gurobipy import GRB
import math
import numpy as np
from matplotlib import pyplot as plt
options = {
    "WLSACCESSID": "xxx",
    "WLSSECRET": "xxx",
    "LICENSEID": xxx,
}
import pandas as pd
import numpy as np
import random
R = np.array([])
for o in range(3,10):
    T = np.zeros((o,3))
    n = np.zeros(3)
    n = np.array([10,15,20])
    Totalmaterials = 15
    beta_0 = 1
    beta_1 = 1
    beta_2 = 1
    def Traveltime():
        random_integer = random.randint(2,4)
        return(random_integer)
    for i in range(0,o):
        for j in range(0,3):
            T[i][j]= Traveltime()
    def Optimize(n,T,o):
        env = gp.Env(params=options)
        model = gp.Model(env=env)
        z = model.addVars(3, lb = 0, vtype = GRB.CONTINUOUS, name = 'z')
        Vi = model.addVars(o, lb = 0, vtype = GRB.CONTINUOUS, name = 'Vi')
        qij = model.addMVar((o,3), lb = 0, vtype = GRB.CONTINUOUS, name = 'qij')
        Pij = model.addMVar((o,3), vtype = GRB.CONTINUOUS, name = 'Pij')
        Qij = model.addMVar((o,3), vtype = GRB.CONTINUOUS, name = 'Qij')
        W = model.addMVar((o,3), vtype = GRB.CONTINUOUS, name = 'W')
        model.addConstrs(Qij[i,j] == beta_0 - beta_1*T[i,j] + beta_2*Vi[i] for i in range(0,o) for j in range(0,3))
        for i in range(0,o):
            for j in range(0,3):
                model.addGenConstrExp(Qij[i,j], W[i,j], "FuncPieces=-2 FuncPieceError=0.01")
        model.addConstrs(Pij[i,j]*sum(W[l,j] for l in range(0,o)) == W[i,j] for i in range(0,o) for j in range(0,3))
        model.addConstr(sum(Vi[i] for i in range(0,o)) <= Totalmaterials)
        model.addConstrs(Vi[i] == sum(qij[i,j] for j in range(0,3)) for i in range(0,o))
        model.addConstrs(qij[i,j] <= n[j]*Pij[i,j] for i in range(0,o) for j in range(0,3))
        model.addConstrs(sum(Pij[i,j] for i in range(0,o)) == 1 for j in range(0,3))
        model.addConstrs(z[j] == n[j]- sum(qij[i,j] for i in range(0,o)) for j in range(0,3))
        obj_fn = gp.quicksum(z[j] for j in range(0,3))
        model.setObjective(obj_fn, GRB.MINIMIZE)
        model.optimize()
        print('Optimization is done. Objective Function Value: %.2f' %model.objVal)
        for v in model.getVars():
            print('%s: %g' %(v.varName, v.x))
        return model.objVal
    R = np.append(R,Optimize(n,T,o)) 

The question is while running the above code for o = 6 it is not able to retrieve attribute 'objVal' and the model is infeasible. But when i solved the problem with another algorithm, I am getting feasible solution for o = 6.

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2026年11月13日 01:24

  This post is more than two years old. Some information may not be up to date. For current information, please check the Gurobi Documentation or Knowledge Base. If you need more help, please create a new post in the community forum, or try Gurobot, our chatbot interface offering instant, expert-level support.
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  Marika Karbstein

  • Gurobi Staff

  2024年05月16日 13:36

  Did you check the article How do I diagnose a wrong result?
  A common issue is that the default lower bound in Gurobi is 0.0 and not -INF as in other solvers.

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  Dhiraj Yadav

  2024年05月17日 03:59

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  Thanks Marika Karbstein. It was really helpful insight about the model.

  Best,

  Dhiraj

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