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120 Topics

X
XinhuiExplorer
asked in Math, OR & Optimization Modeling

Understanding the Differences between MIP and RMIP Solvers

Hi all, I would like to seek clarification regarding the disparities between MIP (Mixed Integer Programming) and RMIP (Relaxed Mixed Integer Programming) solvers. While I understand that RMIP converts integer variables into continuous variables, I would like to explore any other significant dissimilarities between these two solvers.Specifically, I am encountering fluctuations in the results of one of the variables when utilizing the MIP model as shown in the picture below. Despite the absence of any constraint-related issues, the values exhibit variability instead of remaining constant. Conversely, when employing the RMIP solver, the values remain consistent throughout (as presented in picture below). I am keen to understand the cause behind these fluctuations and any significant disparities between the MIP and RMIP solvers that could potentially explain this behavior. Any insights, explanations, or suggestions on how to address these fluctuations would be greatly appreciated too! Than

1
Marcel Hunting
AIMMSian
8 days ago
Wanie Saidi
Wanie SaidiExplorer
asked in Math, OR & Optimization Modeling

Terminated by Solver

Hi,I am solving a huge MIP (481707 integer variables). I set the relative gap to 0% from CPLEX MIP settings. With such a huge model, the solver should take quite some time to solve. Just after 287466.11 sec (3.3 days), the model stop running and the solver status says 'Terminated by solver' why the gap is 1.27%. Why does this happen? I am attaching a screenshot. I'll appreciate any ideas on this. Thanks ! 

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Wanie Saidi
16 days ago
L
LawrenceEnthusiast
asked in Math, OR & Optimization Modeling

My AIMMS version 4.94.3.3 has just two solvers: CBC 2.9 and IPOPT 3.11

Dear AIMMS team, Trust you are doing well. I recently installed AIMMS version 4.94.3.3 and I only found two solvers namely: CBC 2.9 and IPOPT 3.11. I tried adding more solvers to it through the solver configuration but proved abortive. How can I add the following solvers to the version.Conopt, CPLEX, Baron, CP Optimizer, Gurobi, COPT, MINOS, ODH-CPLEX, OCTERATH, PATH, KNITRO, NETSOL. I have also attached the messages I am receiving. Thank you. 

4
Patrick
Administrator
25 days ago
W
waishengEnthusiast
asked in Math, OR & Optimization Modeling

Scenario Based Refinery Logistics Optimisation

Good day, I am facing difficulties as below when I building the refinery logistics model:Sum up the total cost that includes charter rate and ship consumption cost as per the formula below. Note that the calculation can be found in the “Data.xlsx” Make scenario like one of the ship is not working and total ship will be 3 instead of 4. The model should be able to run the total cost based on diff scenarioThe project is about planning the ship route by optimizing the demand fulfilment and total cost from one location to another. I would like to seek some opinion and guidance for me to move on with this project as I am very new to AIMMS. Attached is the project model file for your reference and testing. Do comment if you need more clarification. Thank you and hope to get some response.

0
W
27 days ago
M
MZwanenburg
posted in Math, OR & Optimization Modeling

Capacity constraints in job shop scheduling

Hi all, I am creating a job shop scheduling model in AIMMS for my MSc thesis. The model plans jobs j of production orders i backwards from their due date. The main (nonnegative) decision variables are: StartTime(i,j) = the start time of production order i job j  EndTime(i,j) = the end time of production order i job j The only thing I still need to add is that capacity may not be exceeded. I have the following information: Capacity(j) = total capacity of job j in one time bucket Now I need some counter / variable looking like:x(i,j,t) = the amount processed of operation i, job j in time bucket t. Where time bucket 1 = [0,1], time bucket 2 = [1,2] et cetera. See the figure below for my current data, I want to retrieve the following x(i,j,t) values: x(1,COAT,1) = 0.5 (from 0 to 0.5) x(1,PRO,1) = 0.5 (from 0.5 to 1) x(1,PRO,2) = 0.7 (from 1 to 1.7) x(1,PW,2) = 0.3 (from 1.7 to 2)  x(1,PW,3) = 0.5 (from 2 to 2.5) Does someone have an idea on constraints to retrieve the values for x(i,j,t) a

6
M
1 month ago
L
LawrenceEnthusiast
asked in Math, OR & Optimization Modeling

I want to write conditional statement properly

Dear AIMMS Team,Trust this meets you well? Kindly assist on the problem explained below and find attached the AIMMS file I am working with.   I have a variable StateofCharge(t) in which t is 1 to 24.  I want to place StateofCharge(t) at t = 1 or StateofCharge(01) on the conditional statement below. if ( (Charging_Power_kW(01) + SoCMin) > SoCMax) then     SocMax      elseCharging_Power_kW(01) + SoCMinendif;Note: Charging_Power_kW(01) is put as the value of variable Charging_Power_kW(t) at t=1 While StateofCharge(t) at t = 2,….24 should have the conditional statement below. The index t in the statement applies only from t = 2,….24. If Energy_Difference_kW(t) > 0 then      if (StateofCharge(t-1) + Charging_Power_kW(t)) > SoCMax       SoCMax       else       StateofCharge(t-1) + Charging_Power_kW(t)     elseif (Energy_Difference_kW(t)) < 0 then       if (StateofCharge(t-1) - SoCMin) > Discharging_Power_kW(t)       else        SoCMinendif; Also, if I have a parameter/variable

5
L
1 month ago
M
MarvExplorer
posted in Math, OR & Optimization Modeling

summation over a subset of a period

Hello together,I am a newbie in AIMMs and I need help for my thesis.  t is an index for the period, here t = ( 1,2,3,…,T )How can i set the initial value from E(t=1) = Q How can I implement the E(T+1)  How do i define t=1,…,T-1 Thank you in advance kind regards

0
M
3 months ago
V
vishintoExplorer
posted in Math, OR & Optimization Modeling

Solid Waste Logistics

Problem descriptionProblem related to the transport of urban solid waste, a linear programming problem that aims to minimize the costs of transporting solid waste, obeying municipal generation limits, landfill demand and operating costs. Model descriptionSetsLocalizacao(f) Municipio(i) Transbordo(k) URT(j) Aterro(l)ParametersDistancia1(i,k) Distancia2(i,j) Distancia3(i,l) Distancia4(k,j) Distancia5(k,l) Distancia6(j,l) GeraçãoOrigem(i) CapacidadeTransbordo(k) CapacidadeUTR(j) CapacidadeAterro(l) XCoordenadas(f) YCoordenadas(f) ConstrainsRestGeracao(i)sum(k, QuantidadeTransportada1(i,k)) + sum(j, QuantidadeTransportada2(i,j)) + sum(l, QuantidadeTransportada3(i,l)) = GeracaoOrigem(i)RestTransbordo(k)Sum(i, QuantidadeTransportada1(i,k)) <= CapacidadeTransbordo(k)REstUTR(j)sum(i, QuantidadeTransportada2(i,j)) + Sum(k, QuantidadeTransportada4(k,j)) <= CapacidadeUTR(j)RestAterro(l)sum(i, QuantidadeTransportada3(i,l)) + sum(k, QuantidadeTransportada5(k,l)) + sum(j, QuantidadeTransportad

0
V
3 months ago
C
ChunyangEnthusiast
posted in Math, OR & Optimization Modeling

How can I define a parameter in relation to some elements in the variable

Example:For all t, H(t) = Z(t+1) + Z(t).Z(t) is the variable. And H(t) is the parameter calculated with the adjacent elements in the variable. How can I do this?BTW, in this instance, what’s the ‘index domain’ of the parameter H, as the index t=1,2,……,24, i.e. the maximum element in Z is Z(24), if I define the ‘index domain’ of H as t directly, which means that there exists H(24) = Z(25)+Z(24), which should not be existed. Would this cause error or how can I limit the index domain of H to t = 1,2,…..,23? 

1
Chris Kuip
AIMMSian
4 months ago
luispinto
Administrator
luispintoCustomer Success Manager
posted in Math, OR & Optimization Modeling

Santa 2022 - The Christmas Card Conundrum

Hello All!Santa (actually, I am) is late for Christmas this year. I am starting this thread in the community to discuss implementations and solutions to the Kaggle X-Mas challenge for 2022!For those of you who don’t know, Kaggle it is a site intended for promoting data science through courses and challenges. Every X-Mas they have a special optimization challenge. Last year, I also did some projects for it. You can find more information below on this years challenge in the link below:https://www.kaggle.com/competitions/santa-2022/overviewThis years challenge is to control a 7 linked robotic arm in order to paint a Christmas card.This year, I decided to implement their “Getting started with Santa 2022” workbook (https://www.kaggle.com/code/ryanholbrook/getting-started-with-santa-2022) which provide a naïve way of solving this problem.If you read the workbook you can also see the problem can be transformed to a TSP. Feel free to pickup my first implementation here:https://github.com/luisp

0
luispinto
Administrator
4 months ago
M
MZwanenburg
posted in Math, OR & Optimization Modeling

Job shop problem: capacity constraint and variable if production in time t

Hi all, I am creating a job shop scheduling model in AIMMS for my MSc thesis. The model plans jobs j of production orders i backwards from their due date. The main (nonnegative) decision variables are: StartTime(i,j) = the start time of production order i job j  EndTime(i,j) = the end time of production order i job j The only thing I still need to add is that capacity may not be exceeded. I have the following information: Capacity(j) = total capacity of job j in one time bucket Now I need some counter / variable looking like:x(i,j,t) = the amount processed of operation i, job j in time bucket t. Where time bucket 1 = [0,1], time bucket 2 = [1,2] et cetera. See the figure below for my current data, I want to retrieve the following x(i,j,t) values: x(1,COAT,1) = 0.5 (from 0 to 0.5) x(1,PRO,1) = 0.5 (from 0.5 to 1) x(1,PRO,2) = 0.7 (from 1 to 1.7) x(1,PW,2) = 0.3 (from 1.7 to 2)  x(1,PW,3) = 0.5 (from 2 to 2.5) Does someone have an idea on constraints to retrieve the values for x(i,j,t) a

0
M
4 months ago
W
waishengEnthusiast
posted in Math, OR & Optimization Modeling

Problem on Solving Constraints Mapping

Good day all,I am one of the AIMMS beginners and would like to seek help upon my modelling project that I working on currently.The project is about “Production Planning Optimisation for a High Tech Company” where the company is producing 5 assemblies using 22 materials in the period of 30 weeks.The problem that I am facing while solving this model using AIMMS are as per below:Unable to solve the constraints 6 where at t=0, the onhand inventory must be equal to the input materials during the first week of assemble. The result shows infeasible solution as per below pictures.  I had attached the information of this project for better context. Note that, the similar question/model, can be solve by using python without having any error. And I had attached the reference link below for your reference and comparison. May I know the things that I should double check when running this model ?Appreciate that I can get the respond from you. Thank you. Regards,waisheng  reference link: https://medi

3
M
AIMMSian
5 months ago
Chris Kuip
AIMMSian
Chris KuipAIMMSian
published in Math, OR & Optimization Modeling

Using an API with OpenAPI specification

In this how-to article a hello world style introduction to leveraging a REST API with an OpenAPI specification is presented.  The complete example can be found here.That article discusses creating the attached application. This application can be opened using the AIMMS Community edition. After obtaining an API key from ipTwist, and filling in my own IP address it shows me a location in the Netherlands:  

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J
5 months ago
Jess Es
Administrator
Jess EsCommunity Manager
published in Math, OR & Optimization Modeling

What we're reading (October 2022)

Hello everyone! Check out some interesting reads from the OR and optimization space that are making the rounds here...  Deforestation and World Population Sustainability: A Quantitative Analysis by Mauro Bologna & Gerardo Aquino (via Nature) Global Supply Chains Face Disruption Following Russia’s Invasion of Ukraine by the London business School (via Forbes) Do You Need a Prediction or a Prescription? by Zohar Strinka (via Analytics)  Feel free to share anything good you come across...especially if you or someone you know has published recently!

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Jess Es
Administrator
7 months ago
L
LawrenceEnthusiast
asked in Math, OR & Optimization Modeling

How to select the maximum and minimum value of a variable

Good day All,I have a variable PW(t) where t is index from 1 to 24. What is the command to select the maximum and minimum value of PW(t) and also obtain its average.  Thank you. 

2
L
8 months ago
D
DuMiExplorer
asked in Math, OR & Optimization Modeling

Gantt Chart question

Hello,I´m pretty new to Aimms. I tried to learn to create a Gantt Chart. So I downloaded th example and copied every step in my own program.My question is where can I see the created Gantt Chart after running the program ? Thx

1
gabiservidone
AIMMSian
9 months ago
H
HarmEnthusiast
asked in Math, OR & Optimization Modeling

Machine shop scheduling problem, how to introduce a binaray variable that shows if you have production?

Dear all,I'm quite new to Aimms, therefore I don’t know if my problem is easy to solve or a difficult one. My end goal is to be able to generate an automated production planning for a big pizza bakery. The machine shop scheduling example is in the direction for what I’m looking for, see the link below. https://how-to.aimms.com/Articles/473/473-ProductionPlanning-machinescheduling.htmlThe machine shop scheduling example determines the optimal machine and start time for each order, so that the makespan is minimized. I want to expand this model, so that more contraints can be added. An important binary variable for me is ‘DoYouHaveProductionInAPeriod(i,o,i_hc)’: do you have production at a certain machine i, for a spefic order o, at a certain time period i_hc. An example of a constraint that I want to add and using the variable ‘DoYouHaveProductionInAPeriod(i,o,i_hc)’ is if I have 4 workers available, only 4 machines can run at the same time → for each i_hc, sum((i,o),DoYouHaveProductionI

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luispinto
Administrator
10 months ago
L
LawrenceEnthusiast
posted in Math, OR & Optimization Modeling

Wind turbine Power Modeling with several mutually exclusive variables

Dear All, I want to model the power of wind turbine under different wind speeds with respect to the cut-in, cut-out and rated speeds. How can this be implemented in AIMMS. Please, kindly make your response comprehensive as i am new to AIMMS. Thank you. All the terms have been declared as parameters.  

3
luispinto
Administrator
10 months ago
G
Gloria QuintanillaFormer AIMMSian
published in Sustainabilty & Social Good

Join Our Reforestation Modeling ChallengeNews

Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide. It helps in the fight against climate change by trying to reduce the CO2 levels in our atmosphere.  Popular techniques for carbon sequestration are reforestation and afforestation. They are both similar but slightly different:  Reforestation is restoring forests on lands that were once forests but are no longer, because of deforestation for farming, commercial activities etc.  Afforestation is creating forests on lands that were not previously forests. This could be repurposing land that was used for farming, or mining etc. into forest land.  We at AIMMS have started a new program, AIMMS Forest, to contribute to the fight against climate change.We have partnered with One Tree Planted to support reforestation projects around the world and would like to invite you to join us by participating in this fun challenge. For every person that solves the challenge using an AIMMS model, we will plant 20 trees

218920
Jess Es
Administrator
11 months ago
Jess Es
Administrator
Jess EsCommunity Manager
published in Math, OR & Optimization Modeling

Topic of the Month: Using AI and ML with AIMMS

You may have noticed an item called “Incorporating AI/ML into models” in our recent Roadmap 2022 post. As you probably inferred, that’s Artificial Intelligence and Machine Learning we have in mind. For more on this topic, see also Gertjan’s post: Now we want to hear from you about this topic as we consider the possibilities. How do you (or would you) use machine learning in an AIMMS model? We would be glad to hear your real life examples or ideas as we develop this concept. The more details about your use case, the better! First 5 commenters on this post will get 10 trees planted in their name in the AIMMS Forest! And, of course, all respondents will get our heartfelt appreciation! Even if you don’t have something to say, go ahead and click “like” to let us know you were here ;)  

350
Jess Es
Administrator
1 year ago
Jan-Willem
AIMMSian
Jan-WillemAIMMSian
published in Math, OR & Optimization Modeling

How the AIMMS SC app developers use automated testing

Recently I spoke about automated testing with my colleagues who are developing our off-the-shelf supply chain apps.How and how often do you run the automated tests?Each time we commit AIMMS code to our code repository in Gitlab, an automated pipelineruns our entire test collection. Around 15 minutes later we will know whether any tests failed as a result of the latest code changes.How many tests are in that test collection?We have unit tests and end-to-end tests. For the unit tests we use the AIMMS UnitTest library. For the end-to-end tests we are using a proprietary framework that has been developed in-house and that is being used by several AIMMS teams. For Network Design, for example, we currently have over 450 unit tests and over 400 end-to-end tests, offering us a coverage of about 85%.That is quite an investment, all those tests. What do you get in return?Oh, we get a lot in return. First of all, it makes us feel very confident when we are changing or refactoring code. We cannot

1605
Jan-Willem
AIMMSian
1 year ago
S
samloboExplorer
asked in Math, OR & Optimization Modeling

maximization argument in a minimisation objective Value

Hi All,I would like to write the following equation in my objective variable in AIMMS. I cannot manage to insert a correct notation for the max argument that works. I want to pick the v with the highest value for Zkpv, and minimize this value. My current objective (without the max argument) variable looks like this at the moment.Could somebody please help me? Kind Regards

2
S
1 year ago
D
Dick den HertogEnthusiast
published in Math, OR & Optimization Modeling

Event: Analytics for a Better World Conference (June 1, 2022)Event

Conference Analytics for a Better World | Amsterdam | June 1, 2022  The Amsterdam Business School and analytics and technology company ORTEC have founded the Analytics for a Better World (ABW) Institute in collaboration with Professor Dimitris Bertsimas of the Massachusetts Institute of Technology The institute will work with NGOs, governments and non-profit organizations to contribute to the Sustainable Development Goals of the United Nations such as no poverty, good health and well-being and climate action using data and analytics.» Register now» To the conference websiteConference Analytics for a Better World | Amsterdam | June 1, 2022 About the Conference Who should join? Why should you join? Participation and registration Programme (timezone CET) Register now To the conference website About the ConferenceOn June 1, 2022 (between 14:00-17:10 CET) we are organizing a launching conference to bring together our key partners, researchers and (potential) sponsors. Our aim is to in

420
D
1 year ago
Jan-Willem
AIMMSian
Jan-WillemAIMMSian
published in Math, OR & Optimization Modeling

Call for feedback: Machine Learning and other AI technologies with AIMMS

From quite some AIMMS app developers we have heard demand for ‘enabling AI/ML’ in AIMMS or ‘Run AI/ML, extending the AIMMS platform’. We have ideas how we could indeed deliver this to you. For example:Making it easy to ‘add’ a Python script/program to your AIMMS project that can be fed with model data and from which the results can be returned to AIMMS identifiers. We can think of various ways to run such a Python script, think of Azure Function or maybe as a Docker container, etc.. Making it easy to call ready-to-use services such as ‘Azure Machine Learning’ from your AIMMS model, including the transfer of model data to and from that service.But before we make too many assumptions and start building functionality, we would like to learn more about your needs and expectations.So please tell us: How do you expect AIMMS to support you in applying Machine Learning and other AI technologies, apart from optimization, in your projects? And there is the broader topic. AIMMS has historically f

760
Jan-Willem
AIMMSian
1 year ago
Jess Es
Administrator
Jess EsCommunity Manager
published in Sustainabilty & Social Good

Optimization during the pandemic: an AIMMS-based Vaccine Distribution Planning ApplicationNews

Many organizations now struggle with the task of sourcing and allocating COVID vaccines within their regions.We’ve recently published an interview with Theo Goutier of the Netherlands Municipal Health Services. Goutier, who has led Vaccine Program Operations, tells how they provided vaccinations to those who needed it most while dealing with fluctuating supply and demand, among many other complexities, and what insights they gained from the project.They used an AIMMS-based tool created by our partners at Quomare to:Compute what-if scenarios Determine the optimal number and location of vaccination stations Generate a ‘demand forecast’ for each location Balance required capacity per location, versus expected demand distribution over timeRead details of this case on our Blog: Increasing Speed and Efficiency of Vaccine Distribution During UncertaintyFollowing the success of this tool, a version of such a vaccine-planning application is now available for non-profit use through Math4Good, an

480
Jess Es
Administrator
1 year ago
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