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Research & AIMMS Questions

Ask questions and exchange ideas related to AIMMS modeling — whether you're tackling academic research, exploring algorithmic challenges, or working through AIMMS language and application issues.

  • 158 Topics
  • 358 Replies
158 Topics
J
JacopoExplorer
asked in Research & AIMMS Questions
How to create a new set which is a transformation of a previous set

Basically ill provide here the formulation:We have set t →       t ∈ T = {1,2,...,tn}           ∀t ∈ TAnd we need to create and use set tau where tau stands fortau →      ∀τ =t+1,...,min(t+Li −1,tn) Please, it would be so helpful if someone could provide a solution. Thank you so much.

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luispinto
Administrator
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kimia moosavianEnthusiast
posted in Research & AIMMS Questions
Results

Hello community,I’d really appreciate some help as I’m quite lost. I'm trying to optimize a bi-level system where:The upper level maximizes the leader’s profit. The lower level minimizes consumer costs in an integrated energy system.I received this model from another PhD student, and it should work reliably with three energy types: gas, electricity, and hydrogen. However, I keep getting negative profit in all cases.Following my professor’s guidance, I’m analyzing cost sources to understand why production continues despite negative profits. It seems our revenue doesn’t cover costs such as maintenance, CO₂, investment, and exchange costs.To troubleshoot, I set system capacity to zero to force no production or at least reach a positive result, but it hasn’t worked. Any insights on how to go on? Thanks a lot

626
deannezhang
AIMMS Champ
Wanie Saidi
Wanie SaidiEnthusiast
posted in Research & AIMMS Questions
Clarification on Optimality Gap and Multi-Objective Handling in AIMMS for University Exam Timetabling

I am currently working on a university examination timetabling problem to produce an effective final exam schedule that considers student and lecturer complaints as well as basic scheduling requirements. Upon execution, AIMMS provided a solution with 99.02% optimality, indicating an optimality gap of 0.08% (showed in the progress window). I have a few questions to better understand this result.(1) What exactly does it mean by optimality gap. Does a 99.02% optimality indicates that the solution meets all hard constraints included and is 99.02% optimal relative to an ideal solution? How is this percentage determined. We are curious about whether AIMMS has checked every single hard constraint. (2) Our problems involve 3 objective functions. We are interested to know how AIMMS handles multiple objective functions. Does it calculate each objective function separately or simultaneously? How does this impact the overall optimality percentage? Which objective function might AIMMS be prioritizi

442
Wanie Saidi
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RwitamJEnthusiast
asked in Research & AIMMS Questions
Index issues in a Cutting Stck Model

Hi,I have written one cutting stock model, the constraint is that cutting width should not exceed mother coil width. The indices are mc (mother coil number), mct (mother coil type), bct (baby coil type). Two different bct can be slitted from a same mc and mct.The constraint is thatIndexDomain: (mc,mct)|pMotherCoilTonnage(mc,mct)>0sum[(bct)|pBabyCoilQuantity(bct)>0,vNosBabyCoilMotherCoil(mc,mct,bct)*pBabyCoilWidth(bct)] <= (pMotherCoilWidth(mc,mct) - pTrimLoss(mc,mct))*vMotherCoilSlit(mc,mct).Now the problem is my parameter on trim loss pTrimLoss(mc, mct) is dependent on mc, mct and bct. The trim loss of a ‘mc’ will be differnet for two different bct. I have taken the parameter as pTrimLoss(mc,mct, bct). I am unable to fit it in the constraint. How to address it. 

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Wanie Saidi
Wanie SaidiEnthusiast
posted in Research & AIMMS Questions
Prolonged Execution Time for University Examination Timetabling Problem in AIMMS

Hello,Excuse the long explanation below. We are trying our best to make you understand the whole problem.I am a Masters student currently conducting research on the University Examination Timetabling Problem (UETP) using Binary Integer Programming. The problem is the same examination problem whereby it is to assign exams to suitable slots and venues accordingly to the requirements stated (hard constraints). The number of exams to be assigned, the number of slots available, the number of rooms available are declared as SETS. Also, the same goes for the parameters such as the capacity of each room, students taking specific exams, specific courses that requires 2 hours or 3 hours of exams and etc are known in advanced. We have successfully formulated all the constraints into BIP. Just to let you know that we are executing all models through AIMMS.Below are the constraints and objective functions involved in the model:Constraints: (numbers of constraint below will be used in the table give

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Wanie Saidi
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Mitosz01Enthusiast
asked in Research & AIMMS Questions
OCTERACT error: [json.exception.parse_error.101]

I have run into the following problem, when I was trying to solve my MINLP model. The error massage is the following“OCTERACT error: [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literalWarning: Model status 13: Error no solution, Solver status 9: Error: Setup failure.Warning at line 1 in user-defined function section "MainExecution":Model status 13: Error no solution, Solver status 9: Error: Setup failure.OCTERACT error: [json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - unexpected end of input; expected '[', '{', or a literalWarning: Model status 13: Error no solution, Solver status 9: Error: Setup failure.Warning at line 1 in user-defined function section "MainExecution":Model status 13: Error no solution, Solver status 9: Error: Setup failure.”The strange thing is that with another solver that my teacher got “BARON” it runs just f

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nelson.limaExplorer
asked in Research & AIMMS Questions
Doubts about how to declare specific parts in the definition field

Dear colleagues, I would like to ask for your assistance in order to declare specific parts in the definition field. I have three doubts:1) How to implement a sum in definition in AIMMS in which one of the variables does not start from the first item?Example: i=14j=16(Cprod.Pi,j+Cest.Ei,j)+j=26(Caum.∆Pi,j++Cred.∆Pi,j-) 2) How to implement an expression in definition in AIMMS that considers operations with two subsequent items (in different times)?Example:  Ei,j=Pi,j+Ei,j-1-PDi,j 3) How to implement a value assignment for a specific indexed item in definition in AIMMS?Example: P1,6=1500 Thanks for you assistance.

161
Chris Kuip
AIMMSian
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ccfcuentoEnthusiast
asked in Research & AIMMS Questions
Extracting an index from a variable

t = time indexM = vehicle indexI = supply nodeJ = intermodal nodeI have a variable with (t,M,I,J) index which determines the number of units delivered to a specific node. However, I want to determine the time of delivery of each set of units as a separate variable. Thus, it’s like extracting t from the variables (t,M,I,J). How do I approach this?Thaank you!

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gabiservidone
Administrator
Wanie Saidi
Wanie SaidiEnthusiast
asked in Research & AIMMS Questions
AIMMS License

Hi.I am currently using AIMMS software for my research and have a query regarding the usage of the license I received from AIMMS. Could you please clarify how many machines a single AIMMS license can be used on? Is there a limit to the number of machines where the license can be activated?Thank you in advance for your assistance.

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AIMMSian
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Julia ZimmermannExplorer
asked in Research & AIMMS Questions
Help on Vehicle Routing Problem

Hey everyone,I'm working on a vehicle routing problem (VRP) project where the routing will involve more than one company, and customers may have orders from more than one company. So, the idea would be for the companies to collaborate with each other, and the customer would receive just one delivery.Given the larger set of available companies, I need to use in my constraints subsets that contain only the companies used for each customer. For example, if I have three companies, A, B, and C, how can I create a set with only companies A and B for customer I, another set with companies A and C for customer J, another set with only company B for customer K, and so on?My idea was to create a binary parameter, 1 when the customer requests that company and 0 otherwise. But can I write this parameter in the set definition? I thought about using if and else, but I'm having trouble because the parameter depends on two variables (customer and company) and the company set only on one (company).I'm

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gdiepen
AIMMS Champ
K
kin006Enthusiast
asked in Research & AIMMS Questions
Solving time Octeract and Gurobi

Hello!I have a MIQCP problem that I solve in AIMMS. I have tried to solve it both with Octeract and Gurobi. I solve the same problem with different data sets.For one of the data sets, the solving time for Gurobi is 319 seconds and the gap is 0%, while after 1 hour of solving with Octeract the gap is still 420%.For another data set, the solving time for Gurobi is 1834 seconds and the gap is 0%, while after 1 hour of solving with Octeract, the gap is still 9000%.Does this sound reasonable? I am not that familiar with how these two solvers work, but I thought it was a bit strange that the two solvers give very different results.Thank you in advance :)

381
Marcel Hunting
AIMMSian
J
Jingfan LiuEnthusiast
asked in Research & AIMMS Questions
Whether Set and Element associated with a stochastic Paramater can be use in stochastic optimization

“outage_status(cd)” is a stochastic Paramater, and “outage_units(cd)” is a set and colects u if  “outage_status(cd)” >0. I wonder whether the data of set “outage_units(cd)” will change with the variable “outage_status(cd)” in different scenarios.   

221
Marcel Hunting
AIMMSian
X
XinhuiEnthusiast
asked in Research & AIMMS Questions
Resource balance for resource transport between zones

Hi AIMMS community! I’m currently working on a resource transport model using AIMMS and I've encountered a symmetry challenge for resource balance between zones.In the case when I would like to transport 200MW of power from zone 1 to zone 2, the net outflow of power from zone 2 must be equal to the net inflow of power into zone 1, which can be represented by the equation below:F_in (z,z’) = F_out (z, z’)whereby F_in (z,z’) is represented as the net inflow into zone z (zone 1) from zone z’ (zone 2);while F_out (z,z’) is represented as the net outflow from zone z (zone 2) to zone z’ (zone 1).Does anyone know of an AIMMS function that can seamlessly handle this equation? Any insights or tips are highly appreciated! Thanks so much!

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Dana.PnsgExplorer
posted in Research & AIMMS Questions
Trace the calculation path for the result of the target function

Hello Everyone,I have integrated a vehicle routing problem in AIMMS and was able to solve the model with a case study. I can display the result of the minimized objective function in the Page Manager using a scalar. How can I understand the calculation path for this result? Can I see somewhere which partial results have been calculated for the individual routes or can I display the complete calculation structure? If so, how? Thank you in advance! :)

191
Marcel Hunting
AIMMSian
A
aaahmedExplorer
posted in Research & AIMMS Questions
Multi Depot Multi Vehicles

I am building a multi depot multi vehicle transportation model. The model is running but gives 0 as optimal.I am just about to introduce the vehicles set and this is where i am having trouble now. I want each depot to have two type of vehicles. This is the best way I can get to right now.  I want a set of vehicle type and a set of depot. I want to tell the model that each depot in this example: depot 1 has 2 scooters, and 1 truck, and depot 2 has 3 scooters and 1 truck. Is there a better way to do this, and how to resolve the error. Attached is my model.   

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Dana.PnsgExplorer
asked in Research & AIMMS Questions
Help Opmization Model Vehicle Routing Constraint

Hi Everyone,I need help in implementing an optimization problem concerning the Vehicle Routing in AIMMS.  I am currently indiciating the constraints for the mathematical problem. The index i and j is for the customers or nodes and k is for the vehicles. I now want to implement the constraint, that each vehicle can only leave the material-depot once. The material-depot i indicated by the value “0” for i or j.  The mathematical formulation is now: sum x(0,j,k) <= 1In AIMMS it is indicated as follows: sum(j, x((0,j,k) <= 1)In this case, the index i is directly indicated with the value 0 for the depot but wenn I integrate this formulation in AIMMS, I receive a warning: “The symbol 0 is not expected”.  How can I indicate this formulation in AIMMS in the correct way so that the system understands that “0” is the value for i?  Maybe someone can help me.. Thank you in advance!! :)  

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gdiepen
AIMMS Champ
J
juandelExplorer
asked in Research & AIMMS Questions
Constraint for Variable constancy

First question:How do you make a variable have a consistent value across time? How to make a constraint that will make a variable equal to a previous value likevar(n,t) = var(n,t-1) Second Question:How can you model differently the 9 and 10th constraint?The main function of those constraint are a switch-like event. The constraints ensure that the binary variables for both set will be open, run for a number of time, and then stop.The main difference between the two are for the letter set, the binary variable should be open right from the start which means the binary variable must be equal to 1 at  time = 1. How can you model this differently?  Attached are the additional info about the AIMMS model.

651
gdiepen
AIMMS Champ
L
LawrenceEnthusiast
posted in Research & AIMMS Questions
Robust optimisation for multiobjective functions

Hello AIMMS Team, Trust this meets you well. I want to inject uncertainties into some parameters by using element parameter: "ep_robust" for "AllGeneratedMathematicalPrograms" An element parameter has been declared for the multiobjective optimisation. How do I bring in the ep_robust for the multiobjective function optimisation and individual objective functions optimisation? Your input here will be very helpful. The attached file can be used for the illustration.  Thank you very much.  Regards.

591
gabiservidone
Administrator
T
tschunsExplorer
posted in Research & AIMMS Questions
Transportproblem

Hallo, ich habe 3 Produkte, von 14 Produzenten, die 3 Zielorten zugeordnet werden müssen. Allerdings kriege ich die richtige Verbindung im Modell nicht hin.Dazu habe ich 3 Sets. (K=Produkte, i=Produzent, a=Zielort)Anhand derersten Entscheidungsvariable wird berechnet, welcher Produzent wie viele Mengeneinheiten produziert. (Produktionsvariable)Diese produzierten Mengeneinheiten sollen dann an die drei Zielorte geliefert werden.Das Problem ist, dass ich der Bedarf am Zielort über k gesteuert wird. Aber meine Produktionsvariable steuert sich über i.Wie kann ich denn eine Verbindung modellieren, dass AIMMS versteht, dass i ausgeliefert werden muss, aber das Limit über k gesetzt wird?Bei Bedarf kann ich gerne Screenshots oder den Code einstellen.Danke vorab für jede Hilfe! LGYounes 

543
Chris Kuip
AIMMSian
E
EddyEnthusiast
asked in Research & AIMMS Questions
Help! Optimization Model with multiple products and multi objectives

Hello all together,Unfortunately I am a complete AIMMS beginner and can't get any further on my own.Can someone please help me to build this model (I have only the Academic License):Four products can be produced in a total of 10 locations (but not every product can be produced in every location).All products should then be transported to a fixed location.3 objective functions are to be considered simultaneously with different weights (minimize production costs, minimize CO2 emissions during production, maximize social impact due to production at each location).A few constraints should be taken into account, e.g. if 2 products come from the same location, the transport costs should be reduced, etc. This model should answer the question: how much of which product should be produced in which location? Thanks for your help!

281
luispinto
Administrator
D
duanyilingExplorer
posted in Research & AIMMS Questions
How to make a path selection

Hello everyone. A question that makes me very anxious to ask you all. I am a beginner in AIMMS and have a question for the technicians.I now have 18 nodes ranging from node 27 to node 44 and so on. Some nodes are connected and some are not, as indicated in the program. Now I have to select the paths based on the risk associated with the road (i.e. Building_index in the program), each path has a Building_index and select the combination of paths that has the smallest sum of Building_index from the start point 27 to the end point 44. Finally the solution is solved using MIP.I mainly don't understand the following questions. Any help is appreciated(1) How to select the path that minimizes risk based on connections between nodes (I don't know how).(ii) How to select path segments using binary categorical variables.(iii) How to restrict that there is only one path from node 27 to node 44 with no backtracking in between and the paths must be connected.Attached is a less successful example of

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gmdaniel79Explorer
asked in Research & AIMMS Questions
Adding an Initial inventory in AIMMS

First, let me introduce myself (as its my first post):Im and Industrial Engineer student making my end of master project studying the scheduling of a production plant. My tutor recommended me AIMMS to solve the MIP scheduling problem and, as you might have guessed none of us used this tool ever So far so good, i have found a scientific paper that solves my particular problem ( i dont think i can upload the paper, so I’ll upload only the good stuff)If AIMMS has a good thing its that it was easy (even for me) to introduce most of the constraints and definitions. So i made (most) of themBut theres one that particularly bothers me, restriction (2) and in a lesser way (7). This ones check the inventory stock at the the end of a certain T time, but if T=0, then it check It-1 (which it doesnt exist). And if T=1, it check It=0The thing is that I created a Parameter that holds the Initial Inventory and i wanted to keep as close as the formulation previously showed, so i went ahead and made some

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LGoeckelerExplorer
asked in Research & AIMMS Questions
IF-THEN Batterycharing

Hello to everyone, i have the following problem i can not solve. So on the one side I have consumers that need a certain amount of energy at a time. On the other side I have a generator plant that produce green electricity. The Problem is, that the demand can not alaways be satisfied by the generators. For this I use batteries. The are charged, if there is more then enough energy available.The express this mathematically, I used a if then formulation: For the charging I use:Demand(t) - Generator (t) >= 0 → Battery(t) = Battery(t-1)*(1-self-discharge-coeffizient)+((Demand(t)-Generator(t))*efficiency_Inverter*efficiency_Battery)For the dischargingDemand(t) - Generator (t) <= 0 → Battery(t) = Battery(t-1)*(1 - self_discharge_coeffizient)+((Demand(t)-Generator(t))/efficiency_Inverter)Demand(t), Generator(t) and Battery(t) are variables.self_discharge_coeffizient, efficiency are parameters I do not have any clue how to solve the problem in AIMMS. If anybody could help me, i would be v

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Y
yuyuExplorer
posted in Research & AIMMS Questions
vehicle routing problem that considers soft time windows and fuel costs

I am a novice. I'm working on a vehicle routing problem that considers soft time windows and fuel costs. I need to set a very large penalty value (b) so that it becomes a hard time window because I don't want to violate it. But the solution time will exceed 24 hours. Wondering how to reduce the solution time?The version used is 4.87.3.3. Other versions cannot be used due to research requirements.Thank you for your reply

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Marcel Hunting
AIMMSian
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LawrenceEnthusiast
posted in Research & AIMMS Questions
if else then else condition as constraint/variable, multi-objective optimisation, robust/stochastic optimisation

Dear AIMMS team, I trust this meets you well. Thank you for all your support. My challenge is multifaceted.  I am building AIMMS code to optimize hybrid energy system just as it is presented in the 'calc' sheet of the attached Excel file. The two AIMMS folders attached show how I have attempted to reproduce the 'calc sheet' functions in AIMMS, but below are the comments from AIMMS after running them:   ''The definition of constraint 'Constraint_2(01)' contains an if-then-else statement with a variable in the condition, which cannot be handled by OCTERACT.'' ''The definition of constraint 'Positive_Energy_Difference_kW_definition(01)' contains an if-then-else statement with a variable in the condition, which cannot be handled by OCTERACT.'' All the column functions (in Excel 'calc' tab) are represented in AIMMS. It appears the way I have written the conditional statements in the two AIMMS folders is not allowed. Kindly assist further.  Please note: The AIMMS data file for both AIMMS fol

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