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Math, OR & Optimization Modeling

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120 Topics

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Newest first

cmurray3Enthusiast

published in Math, OR & Optimization Modeling

Help us test a new tool to automatically generate AIMMS code

Hi, Community members, I'm excited to share a new online tool that has been developed by Dowon Lee, a graduate student in Industrial & Systems Engineering at the Univ. at Buffalo, with the generous support of AIMMS. tex2solver generates AIMMS code from LaTeX, or even pictures of an optimization model. In addition to generating AIMMS code, tex2solver also works with Python (using the PuLP package). I'm posting to the Community forum:To publicly thank AIMMS for their support of this project; To let the AIMMS user community know about the free tex2solver tool; and To ask for your assistance to help us test tex2solver.Regarding the last point, tex2solver is still in its development phase. Your feedback is very valuable to help us find bugs and add new functionality. Registration is easy (and free) at https://tex2solver.com. In return, we hope that tex2solver helps streamline your workflow from conceptualizing a model to solving it in AIMMS...like this: Happy optimizing,-chas

9323

3 years ago

Wanie SaidiEnthusiast

posted in Math, OR & Optimization Modeling

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

160

26 days ago

Mitosz01Enthusiast

asked in Math, OR & Optimization Modeling

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

796

1 month ago

ccfcuentoEnthusiast

asked in Math, OR & Optimization Modeling

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!

211

3 months ago

Julia ZimmermannExplorer

asked in Math, OR & Optimization Modeling

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

553

8 months ago

kin006Enthusiast

asked in Math, OR & Optimization Modeling

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 :)

371

9 months ago

aaahmedExplorer

posted in Math, OR & Optimization Modeling

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.

252

1 year ago

Dana.PnsgExplorer

asked in Math, OR & Optimization Modeling

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!! :)

371

1 year ago

juandelExplorer

asked in Math, OR & Optimization Modeling

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.

611

1 year ago

LawrenceEnthusiast

posted in Math, OR & Optimization Modeling

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.

551

1 year ago

tschunsExplorer

posted in Math, OR & Optimization Modeling

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

493

1 year ago

EddyEnthusiast

asked in Math, OR & Optimization Modeling

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!

261

1 year ago

gmdaniel79Explorer

asked in Math, OR & Optimization Modeling

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

592

1 year ago

LGoeckelerExplorer

asked in Math, OR & Optimization Modeling

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

842

1 year ago

yuyuExplorer

posted in Math, OR & Optimization Modeling

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

661

1 year ago

LawrenceEnthusiast

posted in Math, OR & Optimization Modeling

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

670

1 year ago

XinhuiEnthusiast

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

1172

1 year ago

Wanie SaidiEnthusiast

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 !

1562

1 year ago

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.

734

1 year ago

waishengEnthusiast

posted 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.

301

1 year ago

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

1585

1 year ago

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

130

1 year ago

vishintoExplorer

posted in Math, OR & Optimization Modeling

Solid Waste Logistics

260

1 year ago

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?

241

1 year ago

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

450

1 year ago

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