Please correct my code

Answered

Wichitsawat Suksawat Na Ayudhya

• April 18, 2024 13:39

Dear,
I tried to code P-median problem in gurobi by using python, but my code did not show any results. So, please tell me what is wrong with my code. Below is find my code.
Thank you for your quick response.

# Problem data
n=22
p=8
# make a list to creat the number of clients
V = [i for i in range(0,n)]
d={};h={};

for k in range(0,6):
    sheet =book.sheet_by_index(k)
    for i in range(0,n):
        for j in range(0,n):
            d[i,j,k]=sheet.cell(i,j).value

a={};W={}
sheet1=book.sheet_by_index(6)
for k in range(0,6):
    W[k]=sheet1.cell(22,k).value
    
for i in range(0,n):
    for k in range(0,6):
        a[i,k]=sheet1.cell(i,k).value
        
K = [k for k in range(0,6)]
#K = {i for i in range(3)}
#beta = [0.25, 0.20, 0.20, 0.20, 0.20]        
model = Model('P-Median Model')

x,w = {},{}
D ={}
M = {}   
# Add variables
for k in K:
    for i in V:        
        for j in V:
            x[i,j,k] = model.addVar(vtype="B", name="x(%s,%s,%s)"%(i,j,k))
model.update() 

M=model.addVar(vtype="C",name="M-value")

for j in V:
    w[j] = model.addVar(vtype="B", name="w(%s)"%j)

# Constraints
# (2)
for k in K:
    model.addConstr(quicksum(a[i,k]*d[i,j,k]*x[i,j,k]/W[k] for i in V for j in V)<=M)
    
model.update()               
# (3) district i can be served by relief facility j if relief facility j
#     is opened
for i in V:
    model.addConstr(quicksum(x[i,j,k] for j in V ) == 1, "Assign(%s)"%i)
model.update()
# (4) 
for i in V:
    for j in V:
        for k in K:
            model.addConstr(w[j]>=x[i,j,k], name="x(%s,%s,%s)"%(i,j,k))

# (5) total number of facilities to be opened is only P
model.addConstr(quicksum(w[j] for j in V) == p, "Facilities")
model.update()
# Set Parameter for output
model.setParam('OutputFlag',0)
# Compute optimal solution
model.write("2024A.mps")
model.setObjective(M,GRB.MINIMIZE)

0

• 

  Bot Marley (with AI contributions)

  • April 18, 2024 13:48

  

  

  Hi Wichitsawat,

  It looks like there might be a couple of issues in your P-median model implementation.

  1. Model Optimization Call: You have correctly set up the model's objective and variables but have not called the model.optimize() function to start the optimization process. After setting your objective and before writing the model to a file, insert:

  model.optimize()

  2. OutputFlag Set to 0: You have set model.setParam('OutputFlag', 0) which disables Gurobi's logging output. This might be why you see no output even if the model runs. To see Gurobi logs in your console, you can set this parameter to 1.

  - Bot

  0
• 

  Wichitsawat Suksawat Na Ayudhya

  • April 18, 2024 14:04

  

  

  

  Wow. It works.
  
  Thank you so much for your quick response.
  
  P.S. I am an old man who forgot simple rules to make Gurobi code run.

  1

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