# Jacob Jin

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## Activity overview

Latest activity by Jacob Jin
• Jacob Jin commented,

Hi, I have fixed the error and retrieved the extreme ray.  The extreme ray is a 0-vector. It is abnormal. Why gurobi fail to give a valid extreme ray? Thank you so much.

• Jacob Jin created a post,

### Why the extreme ray Groubi retrieved is 0?

During the callback process(benders decomposition),  for one step, when the dual is unbounded, the unbounded ray retrieved by Gorubi is 0-vector. I write this model to an lp file, read and optimize...

• Jacob Jin created a post,

### Can we change the linear expression's lines randomly in gurobi ??

lin_exp_2 = K * sum( z_dual[i, l].x * model.getVarByName('z_' + str(i) + '_' + str(l)) for l in L for i in range(N + 1))+ K * sum(r_dual[i, j].x * model.getVarByName('r_' + str(i) + '_' + str(...

• Jacob Jin commented,

Thanks!

• Jacob Jin commented,

Hi Jaromil,    How could I reset the coefficient of a specific variable in a specific objective function when I deal with a multi-objectives problem in Gurobi?   Thank you so much!

• Jacob Jin commented,

I find the point! from numpy import *import numpy as npimport pandas as pdimport gurobipy as gbfrom gurobipy import *from gurobipy import GRBfrom itertools import permutationsimport timeimport warn...

• Jacob Jin commented,

Hi Jaromi, I have tried your suggestion but it didn't work. The thing I can ensure is that I didn't let the sub_dual problem be preresolved when I defined the objective function in the callback fun...

• Jacob Jin commented,

Hi, Jaromił As for the difficulty we talked about, I realized that when I just set the sub_dual problem's presolve parameter as -1 in the callback function, the log result showed that the solver di...

• Jacob Jin commented,

Sorry for that. Here is the c202.txt.  https://drive.google.com/file/d/1sG4W6F2tGwZ7rTs-TVZOdHh-7FOweXYm/view?usp=sharing  Thank you!

• Jacob Jin commented,

Sorry, I didn't get your meaning about Could you please also incorporate this model change after the first iteration into your snippet to reproduce the issue? My core code:  https://drive.google....