result not correct

回答済み

ghada ouerfelli

2022年02月02日 14:56

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from gurobipy import *
#input data
a=[5 ,6 ,4 ,6 ,7]#
k=['1','2','3'] # bins
C=20 # capacity of bin
#key parameters
N=range(len(a))
M=range(len(k))
#create a model
m=Model('Bin packing')
# create variables
x=m.addVars(N,M,lb=0.0,vtype=GRB.BINARY,name='x')
y=m.addVars(M,lb=0.0,vtype=GRB.BINARY,name='y')
#create constraints
m.addConstrs(x.sum(i,'*')==1 for i in N)
m.addConstrs(x.sum('*',k)*a[i]<=C*y[k] for i in N  for k in M)
#create objective function
obj_fn=quicksum(y[k] for k in M)
m.setObjective(obj_fn, GRB.MINIMIZE)
m.optimize()

the result is: Best objective 3.000000000000e+00, best bound 3.000000000000e+00, gap 0.0000%

and it should be 2 bins 

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• 正式なコメント

  

  Simranjit Kaur

  • Gurobi Staff

  2025年11月16日 23:44

  This post is more than three 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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  Jaromił Najman

  • Gurobi Staff

  2022年02月03日 08:24

  You packing constraint is incorrect. It should read

  m.addConstrs( quicksum(x[i,k]*a[i] for i in N) <= C*y[k]  for k in K)

  This should provide the correct answer.

  Best regards, 
  Jaromił

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  ghada ouerfelli

  2022年02月03日 10:43

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  Thanks a lot Sir 

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