Comments on: Example Models

By: Andrew Mason

Andrew Mason — Tue, 16 May 2023 02:44:42 +0000

A “goal” is a constraint on the objective value, so something that should be faily easy to code up. Good luck, Andrew

By: NAFTALI HERSCOVICI

NAFTALI HERSCOVICI — Fri, 12 May 2023 12:51:01 +0000

Hello Mr. Mason, excellent tool.
I wonder if the goal function can be defined by a macro? If it can, an example would useful.
Thank you

By: Andrew Mason

Andrew Mason — Thu, 21 Mar 2019 21:00:18 +0000

In reply to Alex.

GMPL should just let you pass these parameters, so copy the line above into your SolverStudio model code. Andrew

By: Alex

Alex — Tue, 19 Mar 2019 11:22:01 +0000

Hi Andrew,
I am trying to solve a MIP model (GMPL language), but I want to use the GLPSOL options to limit the search duration (by setting a gap tolerance).

I found this on the GLPK Wiki:
glpsol –cuts –fpump –mipgap 0.001 –model problem.mod –data problem.dat

How can I enter this –mingap functionality in Excel? Since I am here editing the .mod file I believe?

Thanks,
Alex

By: Andrew Mason

Andrew Mason — Tue, 26 Feb 2019 23:25:13 +0000

In reply to Alex.

I suggest you solve the LP first (by relaxing the problem’s integer constraints, ideally via a GMPL option), and then solve the MIP second. Hope this helps. Andrew

By: Alex

Alex — Tue, 26 Feb 2019 14:23:13 +0000

Hi Andrew, when solving my model (language GMPL), I find a optimal LP solution. After this is achieved, the solver also tries to find the MIP optimal solution, which it does. However, I want to output the values of the decision parameters of the LP solution to my Excel file. How can I achieve this?
E.g.:
* 44: obj = 2.211556871e+05 inf = 0.000e+00 (0)
OPTIMAL LP SOLUTION FOUND
Integer optimization begins…
+ 44: mip = not found yet >= -inf (1; 0)
+ 49: >>>>> 3.066614637e+05 >= 2.211556871e+05 27.9% (3; 0)
+ 74: mip = 2.253335908e+05 >= tree is empty 0.0% (0; 17)
INTEGER OPTIMAL SOLUTION FOUND

Thanks in advance

By: Andrew Mason

Andrew Mason — Tue, 22 Jan 2019 19:56:36 +0000

In reply to Pierre Beran.

Any modelling language can do this; just add the “x[i,j]=0” constraints as additional constraints, eg “x[3,4]=0”. Andrew

By: Pierre Beran

Pierre Beran — Tue, 22 Jan 2019 09:47:13 +0000

Hi Andrew,
I have been using opensolver on many instances with great satisfaction. Thank you for making LP available on excel. I have now to solve a problem of the type of the warehouse-bars transportation one, with a large warehouse/bar cost matrix, and would like to use solverstudio for this. In order to speed-up the calculation, I would like to fix to zero some of the elements of the warehouse-bar solution matrix – typically those corresponding to routes too long to be used. Which modeling language should I use to make sure that this variable fixing results in a reduction of the number of optimization variables? I understand that AMPL does this, but AMPL limits the number of variables in its free version. Is there another modeling language -free of use- which shares this feature?

By: Zach de Beer

Zach de Beer — Mon, 09 Apr 2018 13:19:12 +0000

I need to start somewhere but all the language options are confusing. Currently developing an excel spreadsheet with various constraints such as found in a rolling mill (time, yield, speed, weight, lengths, inventory, product,tons, etc) to aid in optimising the throughput in tons. LP seems to be the easier option but
where do I start as a recommendation? Excel solver ad in seems to be expensive for a learner of LP. Regards,

Zach

By: Andrew Mason

Andrew Mason — Mon, 23 Jan 2017 22:13:13 +0000

In reply to Jeff.

No, we don’t have such an example, sorry. Andrew