I am working on a non-linear optimization problem. Even though I wrote the code correctly and it doesn't give an error message, the optimal values are zero. please if there is someone who masters in lingo model help me .
Thank you
Hi
It is due to the definition of constraints and variables
Hello
Is that model a minimization case? If yes, zero is possible. But if it is a maximization case, you may check the consistency of all constraints again. Some constraints might force the objective value to be zero. I hope this will help you.
Dear Sina
I don't think is a Lingo problem
To keep it simple:
Optimal solutions in both linear and non-linear programming, are found at the tangency of one vertex of the polygon of solutions (technically, a convex polytop), with the objective function, either linear (represented by a straight line), or not-linear (represented by a curve).
Therefore, it is absolutely necessary the existence of a polygon of solutions which is formed by all linear constraints, and contains all possible feasible solutions of the problem. The optimal solution is in one of its vertices.
If for any reason this polygone does not exist, the problem is unfeasible, and the Solver in Excel indicates it with a yellow strip and a message.
It is then possible that this is your case, perhaps due to the nature of the actions, i.e., maximization and minimization of constraints.
I suggest to revise the actions in your problem since this could be the cause.
For instance, it is obvious that if in a two constraints problems, one constraint is minmize costs, and the other to maximize benefits, and they don't intersect, there is no solution, but there could be a solution if the do.
Hope it helps
Seyedeh Nafiseh Banihashemi dehkordi
Hi
I defined the constraints in different ways, but unfortunately the results did not change.
Wuttinan Nunkaew
Hi Wuttinan
This is a maximization model. I change the constraints but the desired results is not obtained.
Nolberto Munier
Dear Nolberto
My objective function is nonlinear profit maximization. In the objective function, there are a number of coefficients that, even after changing them, the results did not change much. I rechecked the constraints but I don't think they conflict.
Dear Sina
Well, if you change the coeffcients of the non-linear objective function, there will be a change in the form of the curve, that probably will not have too much influence.
OK. You checked the actions of the restrictions, but did you check that for a max criterion the symbol is =?
If this does not work, could you pls send me the originl ptoblem?
Dear Sima
Thank you for sending me your material
As I told you I don't know LINGO. I work with Solver in Excel.
As a first difference LINGO puts alternatives in rows and criteia in columns, which is exacly opposite as Solver, but of course, it does not influence in the result.
Inspecting your matrix, I notice that are many symbols that you dont say what they mean. For instance
Pi, Yj,Pw, W, Pin
Of course, the sum of performance values for un criterion should be ≤ since you arf maximizying.
An issue that called immediately my attention is the large value for 📷
It appears that there is a contradiction here, because in your first column you establish
📷
📷
The same for the other columns
That is, in one inequation the sum of all performance values in column 1, should be less or equal to 6750, and in the other inequation you say that the weighted sum should be less or equal to 56850000.
Unfortunately, I don’t know the meaning of W, which I guess are weights (although you don’t need weights in LP), but it seems that it must comply simultaneously with two very different values. If it is ≤ 6750, I don’t see how it could be less than 56850000.
Obviously, the result is zero because this is not feasible.
I don’t understand the expression of your objective function. Pls. explain
It would help if I could k now the meaning of each criterion.
I hope it helps