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Academics using AIMMS

A dedicated space for academics and researchers to connect, ask questions, share research insights, and explore academic opportunities with AIMMS.

207 Topics
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Anne2Enthusiast
asked in Research & AIMMS Questions
Minimize (max-min)

Hi, In my model I want to minimize the (maximum_t of a function) - (minimum_t of that function) and I have solved this issue by setting: k >= function for all tp <= function for all tand adding (k-p) to the objective of my model. When I do this for one variable, it works, but: when I do this twice (for different variables and hence adding two variables to the objective) it does not work. This while these variables are not connected. Can anybody maybe help me with this? Thank you in advance!

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HosseinMehdipourEnthusiast
asked in Research & AIMMS Questions
Having multiple solution with AOA

Hello,I am working with the MINLP problem which is solved by AOA in AIMMS. But I get different results whenever I run the code. Could you please tell me why this is happening? I can share my code with you if you need. Please tell me how to upload my code here?Regards

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Marcel Hunting
AIMMSian
R
AIMMS Partner
RogerDaniloAIMMS Partner
asked in Research & AIMMS Questions
Bad scaling threshold default

Hello,I would like to know if there are any  theorical references of why the default value of the bad scaling threshold is  “1000”, or this default is due to the many yeras of experience of the Aimms developers? 

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Marcel Hunting
AIMMSian
H
HosseinMehdipourEnthusiast
posted in Research & AIMMS Questions
Setting initial point (solution) for CONOPT solver

Hello,I am solving a nonlinear problem in AIMMS using CONOPT solver and I need to set the initial solution. I have read the AIMMS language reference and also surf the internet for solving this issue. But according to  AIMMS website only CPLEX, GUROBI and CBC support solving with an initial solution. Could you please tell if there is any way to set the initial solution for CONOPT or any other “nonlinear” solver?

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Marcel Hunting
AIMMSian
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sineplexusExplorer
asked in Research & AIMMS Questions
specific constraints vehicle routing

Hello guys,   currently im doing a Project at my University. I have to do a Simulation Pretty simular to the tutorial for begginers.  But i have some more constraits which i have to imply but have no clue how to.code theese. In General: I have to get my products to the different customers. but i just have one “car” with a set storage. the case is, that the car definetly Needs to drive sometimes back to the warehouse, but i want to optimize the Situation.  for example: i can fit product a for customer a in the car. and the half of product b for customer b. so i want to know whether it is more worth driving back and then Picking up the whole product for customer b. or is it more worth to immediately drive to customer b and in the 2nd route i allready can pick up e.g. product c for customer c.  In Addition to this: i also want to imply, that there is a amount of time needed to put the products in and out of the Vehicle.  My native language is not english, but i hope you could understa

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mohansx
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XuboExplorer
asked in Research & AIMMS Questions
Modelling Question - if-then constraint

Dear all, I would really like to seek for your kind help regarding an if-then constraint. I found in the community a similar topic but my condition is a bit different from that, therefore I want to show my case and ask for your tips again.   Specifically, I have the following variables: A: decision variable B: variable Q: variable   And I want to achieve the following: 1)if A-B>=0, then Q=A-B 2)if A-B<0, then Q=0   I would like to ask if it is possible to consrtuct a linear formulation for this if-then logic to be realised.   Many thanks in advance! Xubo  

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Marcel Hunting
AIMMSian
krzysztof_postek
krzysztof_postekExplorer
posted in Research & AIMMS Questions
Robust optimization - applied project guidelines

Tutorial document (4 pages, 1 scheme, for download)   Would you like to check how robust are your optimized decisions, if possible, construct better ones? Every project is different, with new people to be introduced to the idea, and it is handy to have a step-by-step guide on what to do to construct a new algorithm (see below a table, a file to download is attached).   I am an assistant professor of Operations Research at the Erasmus University Rotterdam, doing mostly robust optimization. Based on the internship OR projects of my students, I wrote a short tutorial with key steps to define what exactly is needed, and about what to think in advance. Its aim is to help with such projects in the future and give a guidence “what to look for”.   I hope the attached document is useful for your work. Any comments or criticism are welcome!   Best, Krzysztof     Step Questions to answer 1. How are solutions determined now? What are the

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Gertjan
AIMMSian
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HosseinMehdipourEnthusiast
posted in Research & AIMMS Questions
Warning: Model is not yet optimal

Hello, I have implemented the simple nonlinear problem in AIMMS which uses the CONOPT 4.0 solver to solve it. But whenever I run the code, the objective function value changes and I get the warnings like:   "Warning: After 252 iterations CONOPT 4.0 terminated and BasicStateEstimation is not yet optimal. The minimum found for obj is 704.122936573."   It seems that the optimization procedure stops before convergence. Therefore, I checked the "stop criteria" from the "solver general" and "specific solver" icons and changed some of them, but I still have the same issue. Would you please tell me how I can solve this issue? Please let me know if you need the code.   Regards

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Marcel Hunting
AIMMSian
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Max Lomba VrouenraetsEnthusiast
asked in Research & AIMMS Questions
Robust Optimization

Hi, After building a deterministic model, I constructed the robust counterpart of the model. I defined an uncertain parameter and I called the GMP  GenerateRobustCounterpart. The model seems to be running without errors,however, it does not provide any result. It seems like the variable (vAllcocationFlow) does not get filled. Can someone help me with this? I attach you here the Solve function (1) and the uncertain parameter definition (2):   Thank you very much in advance!

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Kostas Vasilakakis
Jess Es
Jess EsGrand Master
published in Modeling for Impact
Webinar: Analytics for a Better WorldEvent

Join the second Analytics for a Better World Webinar (ABW-W)    Wednesday - May 27, 2020   17:00PM-18:00PM Central European time 8:00AM-9:00AM Pacific time 11:00AM-12:00PM Eastern time     Speakers:Koen Peters, Head of Development for Supply Chain Planning at World Food Programme (WFP)  and PhD at Zero Hunger Lab, Tilburg University, The NetherlandsHein Fleuren, Professor in applying Business Analytics at Tilburg University, The Netherlands, and director Zero Hunger Lab   Title:  “Dear mathematician: why are you here? We need to move tonnages and help hungry people!” In this webinar we will highlight Tilburg University’s (The Netherlands) work at the United Nations - World Food Programme (WFP) headquarters in Rome. WFP is the largest humanitarian agency fighting hunger worldwide, reaching around 90 million people with food assistance in 80 countries each year.    By connecting traditional supply chain elements to nutritional objectives, we made significant breakthroughs in the operatio

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mazaExplorer
asked in Research & AIMMS Questions
Excel

I am a beginner. I have created my model and now I need to read data from Excel. I have tried following the “ReadingExcelData.ams” example and specifically AXLL, but it doesn't work and keep getting this error: “The first argument of internal procedure "ReadUsingAXLL" must be an explicit identifier.” In fact, when I run the “ReadingExcelData.ams” example itself, it doesn't show me the data that model was supposed to read from excel. so my second question is how should I get the example work? Really appreciate any help with this. Thanks

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Jess Es
Jess EsGrand Master
published in Research & AIMMS Questions
Webinar: How to improve the adoption of Robust Optimization by practitionersEvent

Join the next Robust Optimization Webinar - ROW Talk!   Date: WEDNESDAY, May 20, 2020 Time: 9.00-10.00 Boston time, 15.00-16.00 Dutch time, 21.00-22.00 Singapore time.   Featured speaker:  Dick den Hertog (Tilburg University, Tilburg, The Netherlands)   Panelists:  Aharon Ben-Tal (Technion, Haifa, Israel) Dimitris Bertsimas (MIT, Cambridge, USA) Frans de Ruiter (CQM, Eindhoven, The Netherlands)   The three panelists will react on Dick den Hertog's topic, How to improve the adoption of Robust Optimization by practitioners, followed by a plenary discussion.   Zoom link:  https://ethz.zoom.us/j/451585177 (for more joining options, see below) Join Zoom Meetinghttps://ethz.zoom.us/j/451585177 Meeting ID: 451 585 177 Dial by your location         +1 786 635 1003 US (Miami)         +1 213 338 8477 US (Los Angeles)         +1 253 215 8782 US         +1 312 626 6799 US (Chicago)         +1 470 250 9358 US (Atlanta)         +1 646 518 9805 US (New York)         +1 669 219 2599 US (San Jose) Meet

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Jess Es
Gertjan
AIMMSian
GertjanChief AIMMSian
posted in Research & AIMMS Questions
Linear Programming exercises

Came across a nice set of (3) Linear Programming exercises from the Erasmus University of Rotterdam (academic year 2016/2017) that might interest you.  https://www.studeersnel.nl/nl/document/erasmus-universiteit-rotterdam/lineair-programmeren/verplichte-opgaven/exercise-set-aimms-16-17/999425/view

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Gertjan
AIMMSian
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Gloria QuintanillaFormer AIMMSian
published in Modeling for Impact
Supporting the Dutch Healthcare System with AIMMS-based Optimization During the COVID-19 PandemicBlog

This article is based on an interview with Erwin Hans, Professor of Operations Management in Healthcare at the University of Twente and Co-Founder of CHOIR and Rhythm B.V. Erwin is helping care givers address the challenge of critical care capacity and is looking for motivated students with AIMMS know-how to join the effort!  AIMMS and I have a long-standing relationship. As a former student of applied mathematics at the University of Twente, an institution where I now teach, I completed my graduation project under the supervision of AIMMS’ founder, Johannes Bisschop. Jan, as we call him, was my thesis supervisor. My path in OR started at the Energy Research Foundation in the late 90s. During my time here, I conducted my master’s research on the liberalization of the European electricity market. Specifically, I developed an AIMMS-based model to understand how electricity transport, post liberalization, would impact prices. After completing my research, I took on a PhD position in logis

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Yoyo1Newcomer
asked in Research & AIMMS Questions
Warning: Model status 13: Error no solution, Solver status 9: Error: Setup failure (see message window).

Hello everyone, I am currrently doing a project for my university and  I have this type of error :  CPLEX cannot handle MIQCP models with quadratic equality constraints like 'BtoWCosts_definition(91789)'. I checked all my variables and my constraints but couldn’t find any “quadritic” ones.  And the error message tell me the error is in the definition of the variable “BtoWCosts” but again I can changed a lot of thing  and It still didn’t work.  Here is the definition “ BtoW(W)* (NumberTrucks(W)*Truckload(W) )” where Btow(w) is binary and the 2 others Intergers… Thanks You in advance, Yoyo1

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amadeodumExplorer
posted in Research & AIMMS Questions
Extended formulation returns infeasible

Hello everyone, I am currently working on a Supply Chain problem (LS-U-B) and I am facing some issues that I can not solve. I have a standard formulation where the objective funtion is to minimize the total costs (Inventory and Backlog).  The “classical” flow constraints are:  Intenvory(s-1) + Production(s) + Backlog(s) =Demand(s) + Inventory(s) + Backlog(s-1) where s is the period (from 2 to 10).  Production(s) + Backlog(s) = Demand(s) + Inventory(s) where s is the period (at time t=1) The standard model is running as it should without problem. However, I have to build an extended formulation for this constraint (strenghten the formulation) and it does not work.  To do so, I created a new variable Production(s,r) representing the Production done at period s for the demand period r.  Consequently, the following variables are:  Inventory(s) = sum[r|ord(r)<=ord(s), sum[y|ord(y)>=ord(s)+1, Production(r,y)]] Backlog(s) = sum[r|ord(r)>=ord(s)+1, sum[y|ord(y)<=ord(s), Production(

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Andrew
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Max Lomba VrouenraetsEnthusiast
asked in Research & AIMMS Questions
Reading excel data

Hi,   I have built my first AIMMS model and it is running without any errors now. However, it does not read my excel data and therefore I do not get any result. I was wondering what could be the problem. Do I need to save the project and the input excel sheet in the same folder?   Thank you very much in advance!  

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Farhan SururyEnthusiast
posted in Research & AIMMS Questions
Ant-Colony Optimization

Dear All, I want to develop Routing Problem Model using Ant-Colony method, does AIMMS possible to generate the method? Are there any example that anyone could share..?   Thank you very much  

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F
A
arasselviNewcomer
asked in Research & AIMMS Questions
Global Optimization Solver Lower-Upper Bounds

Dear AIMMS Community:   I am using BARON solver to solve a continuous non-convex optimization problem. In small cases, I can see that BARON is finding the global optimum and wherever it is verifiable I am verifying that the results are consistent. So I believe my current modeling is correct.   However, for larger problems, although I get a feasible solution, I don’t have any upper bounds (this is a maximization problem). I found this post, and tried problem.BestBound, which gives NA as answer. How can I fix this issue? Many thanks for your time!

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juliolema
AIMMS Partner
juliolema
posted in Modeling for Impact
COVID-19 relief efforts: pro bono support.

Dear all, I write on behalf of baobab soluciones, an AIMMS partner based in Madrid.  Since the onset of the pandemics we have decided to support organizations and public authorities and offer our solution development services pro-bono for crisis relief projects. We were thinking route optimisation, workforce optimisation, workload management, load balancing between centres, for healthcare, quick response and critical supply chains. Quick, technically simple projects that will help take the most out of our exhausted common resources. So if you encounter a situation where we can be of assistance, please do not hesitate to contact us. Thank you very much, Julio

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juliolema
AIMMS Partner
M
ManuelExplorer
asked in Research & AIMMS Questions
Indexing a variable with an initial value or constraint

Hi everyone. I'm starting with Aimms, I have two questions   First How can I index a variable with an initial value or constraint? . For example X (i) is the dependent variable of the set (for example 4 things) with index i. And what I need is X (1)> = 50 X (2) <= 250   Variable X {     IndexDomain: i;     Range: nonnegative; }   Second How can I implement or call benders decomposition modules, stochastic programming etc. inside the MainExecution procedure? Thank you Thanking you for your support.

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M
Aanand
AIMMSian
AanandAIMMSian
published in Modeling for Impact
Study 5Knowledge Base

Study 5: Refine Capacity Smoothing This study can help you ensure resource requirements in your supply chain. Impact – As certain resources are forced to close, other resources will experience an increased load. Companies may not be able to adequately ramp up capacity and lose sales.  Action – Inventory must be kept in anticipation of resource unavailability in the future. At the same time, over-utilization must be reduced to not exhaust the resources. How –AIMMS S&OP Navigator enables users to perform capacity smoothing. This incurs a penalty on over-utilization and tries to minimize it by ensuring that inventory has been built up in anticipation of future shortages. It also suggests alternative distribution options for obtaining the product in case the resource in question is unavailable. Demo –Capacity Smoothing in S&OP Navigator This article is part of the series Immediate Supply Chain Actions to Take Amid COVID-19.

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Aanand
AIMMSian
Aanand
AIMMSian
AanandAIMMSian
published in Modeling for Impact
Study 4Knowledge Base

Study 4: Create Multiple Plans for Resource Utilization This study can help you ensure resource requirements in your supply chain. Impact –Manufacturing plants and warehouses will experience a sudden shift in resource utilization. There will most likely be a reduction in labor hours as fewer people will work in a closed, crowded environments. This could even lead to total shutdown of certain plants. Action – Study multiple resource utilization what-if scenarios and accommodate your production plan accordingly.  How – S&OP Navigator allows users to simulate changes in resource capacity, labor hours, utilization, production lines and throughput rate dynamically within the application. The output is a detailed production and distribution plan that maximizes your margin. Note:If using your own bespoke app, another option is to re-adjust your objective function. We have seen this work very well in the past where a customer, during a crisis, moved from Production Maximization to Cost Min

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Aanand
AIMMSian
Aanand
AIMMSian
AanandAIMMSian
published in Modeling for Impact
Study 3Knowledge Base

Study 3: Identify Optimal Sourcing Locations This study can help you anticipate shortages in your supply chain. Impact – As transportation lanes become unavailable, the availability of suppliers and components will decrease.  Action – There is a strategic incentive in understanding the optimal sourcing location for specific customers, and in understanding the optimal sourcing location for the different resources. This is not to say that there is no value in having multiple supplier options, but understanding who your ideal supplier is can enable you to form the right relationship and expectations with them for the coming weeks.  How – Network Design Navigator enables forcing a single source as a constraint. Once the constraint is relaxed, customers are free to choose from a multitude of suppliers. However, with the constraint enforced, the optimal source of the product can be studied while minimizing both production and distribution costs. Network Design can also be used to make certai

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Aanand
AIMMSian
Aanand
AIMMSian
AanandAIMMSian
published in Modeling for Impact
Study 2Knowledge Base

Study 2: Inspect Demand Trends This study can help you understand exposure in your supply chain. Impact –Since demand will significantly fluctuate and spike for a period of time before reverting to the mean, accurate demand signaling for the future becomes a challenge. Misreading these signals often leads to the bullwhip effect. When shoppers decide to hoard all the toilet paper from the stores, it sends a signal through the supply chain to produce more. If the toilet paper companies decide to produce more, extra inventory is pushed into the distribution channel. Inevitably, demand will stabilize and when it happens, the stores will find themselves overstocked since customers are still exhausting their previous purchases. Action – Demand trends must be studied closely and any outliers must be treated to avoid inaccurate resource planning for the future.  How – AIMMS Demand Forecasting Navigator can be used to perform time-series analysis for individual product groups. Machine learning

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Aanand
AIMMSian
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