CODEWITHSUNDEEP
python-3.xcplexdocplex
S.Perera
S.Perera

Reputation: 904

DOcplexException: Expression xx cannot be used as divider of xxx

I am new to CPLEX and I was trying to find an example where the decision variable is in the denominator of the objective function but couldn't. My optimisation problem;

enter image description here

I have tried the following on Python3;

from docplex.mp.model import Model
import numpy as np
N = 1000
S = 10
k = 2

u_i = np.random.rand(N)[:,np.newaxis]
u_ij = np.random.rand(N*S).reshape(N, S)
beta = np.random.rand(N)[:,np.newaxis]

m = Model(name = 'model')
R = range(1, S+1)

idx = [(j) for j in R]
I = m.binary_var_dict(idx)
m.add_constraint(m.sum(I[j] for j in R)<= k)

total_rev = m.sum(beta[i,0] / ( 1 + u_i[i,0]/sum(I[j] * u_ij[j,i-1]  for j in R) ) for i in range(N) )

m.maximize(total_rev)
sol = m.solve()
sol.display()

However Im getting the following error when running the line;

total_rev = m.sum(beta[i,0] / ( 1 + u_i[i,0]/sum(I[j] * u_ij[j,i-1]  for j in R) ) for i in range(N) )

Error :

DOcplexException: Expression 0.564x1+0.057x2+0.342x3+0.835x4+0.452x5+0.802x6+0.324x7+0.763x8+0.264x9+0.226x10 cannot be used as divider of 0.17966220449798675

Can you please help me to overcome this error?

Upvotes: 0

Views: 193

Answers (1)

Alex Fleischer
Alex Fleischer

Reputation: 10062

Since your objective is not linear you should use CPO within CPLEX

from docplex.cp.model import CpoModel



import numpy as np
N = 10
S = 10
k = 2

u_i = np.random.rand(N)[:,np.newaxis]
u_ij = np.random.rand(N*S).reshape(N, S)
beta = np.random.rand(N)[:,np.newaxis]

m = CpoModel(name = 'model')
R = range(1, S)

idx = [(j) for j in R]
I = m.binary_var_dict(idx)
m.add_constraint(m.sum(I[j] for j in R)<= k)

total_rev = m.sum(beta[i,0] / ( 1 + u_i[i,0]/sum(I[j] * u_ij[j,i-1]  for j in R) ) for i in range(N) )

m.maximize(total_rev)

sol=m.solve()

for i in R:
    print(sol[I[i]])

works fine

Upvotes: 1

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