The problem of solving AMPL

[Cai Gangying]

Dear professors, when I used AMPL to solve the model, the following questions appeared: (1) Can AMPL directly solve the programming problems with norm constraints? My treatment is: for example, for the infinite norm x≤y, I simply remove the absolute value so that every component of the vector x is ≤y, x_i≤y,-x_i≤y; For 1 norm x less than or equal to y, introduce two auxiliary variables a,b, let x=a-b, then the absolute value of x=a +b,a,b≥0, after linearizing the norm constraint, find the dual problem of the original problem, may I ask whether this treatment is correct? (2) Solutions obtained by different solvers are completely different. For example, for solving the same model, which I consider to be a linear convex optimization problem, I want to compare the solution results of different solvers, but I find that the solutions obtained by local solvers minos, knitro and global solvers baron differ greatly. Even the results between minos and knitro are quite different. It can be said that the results obtained with any kind of solver are quite different from each other. Please kindly answer the reasons for this and tell me where to find the problem and correct it. (3) If possible, I would like to ask you to check my model and data files. Could you please not send them to the group? As this is a work in progress, I would appreciate it if you could provide your personal email address! Looking forward to your reply, I wish you all the best!

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On Wed, Jun 5, 2024 at 3:24 AM UTC, AMPL Modeling Language <am...@googlegroups.com> wrote:

Dear professors, when I used AMPL to solve the model, the following questions appeared: (1) Can AMPL directly solve the programming problems with norm constraints? My treatment is: for example, for the infinite norm x≤y, I simply remove the absolute value so that every component of the vector x is ≤y, x_i≤y,-x_i≤y; For 1 norm x less than or equal to y, introduce two auxiliary variables a,b, let x=a-b, then the absolute value of x=a +b,a,b≥0, after linearizing the norm constraint, find the dual problem of the original problem, may I ask whether this treatment is correct? (2) Solutions obtained by different solvers are completely different. For example, for solving the same model, which I consider to be a linear convex optimization problem, I want to compare the solution results of different solvers, but I find that the solutions obtained by local solvers minos, knitro and global solvers baron differ greatly. Even the results between minos and knitro are quite different. It can be said that the results obtained with any kind of solver are quite different from each other. Please kindly answer the reasons for this and tell me where to find the problem and correct it. (3) If possible, I would like to ask you to check my model and data files. Could you please not send them to the group? As this is a work in progress, I would appreciate it if you could provide your personal email address! Looking forward to your reply, I wish you all the best! --