Gurobi/python: infeasible model
回答済みI have a model m . I want to code the two constraints shown in the figure correctly.
- The different set of data are as follows:
```
R = [1,2,3,4]
K = [1,2]
P = [1,2,3,4]
D = [5,6,7,8]
PD = P + D
C = [10,11,12,13,14,15,16,17,18,19,20,21]
PDC = PD + C
Cr = {1: C[0:3], 2 : C[3:6],3: C[6:9], 4: C[9:12] }
O = [0,9]
N = O + P + D + C # all nodes
OC = O + C
# The parameter f:
fr={}
for r in R:
for i in N:
fr[r,i] = 1 if i in P else -1 if i in D else 0
# the variables
yr = m.addVars(R,N,N, vtype=GRB.BINARY)
z = m.addVars(((r,i,j) for r in R for i in Cr[r] for j in Cr[r]), vtype=GRB.BINARY, name='z')
print(z)
I want to know whether the next two constraints are programmed correctly
```
m.addConstrs((quicksum(yr[r,i,j] for j in N) +
quicksum(z [r,i,j] for j in Cr[r])-
quicksum(yr[r,j,i] for j in N )-
quicksum(z [r,j,i] for j in Cr[r]) == fr[r,i] for r in R for i in Cr[r] ),'6')
m.addConstrs((quicksum(yr[r,i,j] for j in N if j!=i)-
quicksum(yr[r,j,i] for j in N if j!=i)== fr[r,i] for r in R for i in N if i not in Cr[r] ),'7'')
```
when I run the code I get a message says infeasible model. When I used the
m.computeIIS()
m.write("irreducible.ilp")
I get about 25 constraints/bound problem, but I think the problem resides in the above two constraints because when I tried to formulate them with a different method I get the infeasibility message but with 2 constraints/bounds.
the other way I used as follows:
```
m.addConstrs((quicksum(yr[r,i,j] for j in N) +
quicksum(z [i,j] for j in Cr[r])-
quicksum(yr[r,j,i] for j in N )-
quicksum(z [j,i] for j in Cr[r]) == 0 for r in R for i in Cr[r] ),'6')
m.addConstrs((quicksum(yr[r,i,j] for j in N if j!=i)-
quicksum(yr[r,j,i] for j in N if j!=i)== 1 for r in R for i in P ),'7-')
m.addConstrs((quicksum(yr[r,i,j] for j in N if j!=i)-
quicksum(yr[r,j,i] for j in N if j!=i)== -1 for r in R for i in D),'7')
m.addConstrs((quicksum(yr[r,i,j] for j in N if j!=i)-
quicksum(yr[r,j,i] for j in N if j!=i)== 0 for r in R for i in OC if i not in Cr[r] ),'7+')
```
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正式なコメント
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Hi Sabrin,
I would take a look at fr and print out if this dictionary looks like expected.
Best,
Sonja
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Sonja, thanks a lot for your prompt reply. I have printed out the fr, constraint 6 and constraint 7. The output seems acceptable and the constraints correctly captured the required nodes. However, the code I wrote returns back an infeasible model message.
I really need urgent help!!!!!!!!!!!!!!!! please. I do not know why the model is infeasible and what is wrong. I can share the whole code along with the model itself which is published in a reliable journal.
I feel it is a trivial issue that can be captured quickly if I shared the whole code, but it should not be publicly.
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Hi Sabrin,
From this post it seems you got it working now. Can you share what you did for solving it?
Thanks,
Sonja
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Hi Sonja, the infeasibility was due unreasonable quantity of a particular parameter (input data). This is how I thought to catch the error: after employing m.computeIIS() and m.write("irreducible.ilp"), it has become clear for me the constraints contributing to the infeasibility. I revised and studied them carefully and with little logic and thinking I realized that the infeasibility was due unlogic quantity of a specific parameter.
Now the model is working but takes a too long time. To solve it faster, I am going to implement three different techniques ( arc elimination, subtour elimination, and variable substitution). These will be challenges that I should face, it is my first model to solve!!
Regards,
Sabreen
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