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I would like to import this file http://people.brunel.ac.uk/~mastjjb/jeb/orlib/files/scp61.txt . Does CPLEX support this format in Python? I converted the text file to a CSV file then wrote this code cplex.read("scp61.csv") but I got this error"CPLEX Error 1436: Max or Min missing."
There isn't any Max or Min word in the text file.

Alex Fleischer
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CPLEX-user
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  • description of the error : The objective function sense indicator is missing from the LP file. No problem is read. source : https://www.rpi.edu/dept/math/math-programming/cplex66/sun4x_56/doc/refman/html/appendixC.html – ayoub mlaouah Jan 31 '21 at 22:33
  • I know but the file is a benchmark problem. I can't change it. – CPLEX-user Feb 01 '21 at 06:05

2 Answers2

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scp61 contains the data but not the model.

In python it's possible to parse the file and then call cplex through the docplex python API.

from docplex.mp.model import Model


file = open('scp61.txt', 'r')
count = 0

values=[]
print("Using for loop")
for line in file:
    count += 1
    ar=line.split()
    for i in ar:
        values.append(int(i))
 
file.close()

n=values[0]
m=values[1]

print("n=",n)
print("m=",m)

values2=values[2:]

mdl = Model(name='scp')

#decision variables
x=[mdl.binary_var(name='x'+str(i)) for i in range(1,m+1) ]

#objective
mdl.minimize(mdl.sum(x[i-1]*values2[i-1] for i in range(1,m+1)))

index=0
index=index+m
i=0

while (index!=len(values2)):
    
    i=i+1
    nbr=values2[index]
   
    index=index+1
    which=[]
    for j in range(0,nbr):
        index=index+1
        
        
        if index==len(values2):
            break
        which.append(values2[index])
    #constraint    
    mdl.add(1<=mdl.sum(x[j-1] for j in which),"ct"+str(i))

mdl.solve(log_output=True,)

for v in mdl.iter_binary_vars():
    if (v.solution_value!=0):
        print(v," = ",v.solution_value)
Alex Fleischer
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DOcplex supports three model formats: LP, SAV and MPS for MP models, plus CPO format for CP problems.

For other formats, you need to write custom reader code to import to a DOcplex model, as Alex did in the above post.

Philippe Couronne
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