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Algorithmic Capabilities & Optimization Modeling

Get and give help about Algorithmic Capabilities and Optimization Modeling.

  • 15 Topics
  • 58 Replies
15 Topics
Wanie Saidi
Wanie SaidiEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
Long Execution Time

Hi,I am working on a University Examination Timetabling Problem (UETP) using Binary Integer Programming, and I am running the model in AIMMS. The model is taking an unexpectedly long time to solve.Previously, I set the optimality relative tolerance to 0.01, and while the results were not 100% optimal, I was able to obtain optimal solutions in a reasonable amount of time. However, when I set the optimality relative tolerance to 0, the model has been running for an extended period. After 5 to 9 days, the gap was 0.38%, and after 10 to 16 days, the gap only reduced to 0.37%, this model still running.I ran this model on two different machines to compare performance, and both showed similar results:Server: Intel(R) Xeon(R) Silver 4214 CPU @ 2.20 GHz (2 processors), 16 GB RAM, Windows 10 Pro Desktop PC: 13th Gen Intel(R) Core(TM) i7-13700 @ 2.10 GHz, 64 GB RAM, Windows 11 ProMy questions are:What could be causing such a long execution time with this model? Are the specifications of these mac

592
Wanie Saidi
1 month ago
J
Jingfan LiuEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
Create a FUNCTION with multiple input and output.

Hi! Does anyone know how to create a function with multiple inputs and outputs?For example, there is a function edited with MATLAB that :“function [ dP,dQ,Pi,Qi ] = Unbalanced( n,m,P,Q,U,G,B,cita )”. How to model this function in AIMMS? Thank you very much! 

203
Chris Kuip
AIMMSian
2 months ago
Wanie Saidi
Wanie SaidiEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
Terminated by The Solver

Hi,I am solving a huge MIP (4446310 integer variables). I set the relative gap to 0% from CPLEX MIP settings. After 69532.16 sec (19.3 hours), the model stops running and the solver status says 'Terminated by solver' while the gap is 0.14%. Why does this happen? What are the possible causes? Thank you. Best regards,Wanie Saidi 

24921
Wanie Saidi
4 months ago
L
liv.stgExplorer
asked in Algorithmic Capabilities & Optimization Modeling
Help with implementing optimization model

Hello,I need help with implementing my model in Aimms. I want to implement a work staff optimizing model with on-call services. I want to show that on call-services can help with temporary bottlenecks and variable demand.Sets:t – Periodsj - LayersParameters:a (t,j) – Period of useb (t) – Staff requirementsVariables:x (j) – regular employeesk (j) – on-call-services employees This ist the optimizing model:minj=1Jxj+kj  These are my constraints:Demand fulfilment:J=1Jatj×xj+kj≥ bt                                     ∀t Deployment of employees:(x(j)+k(j))>= 1xj∈N                       ∀j kj∈N                         ∀j   I wanted to implement it like this:Set Periods {             Index: t;       }       Variable x {             IndexDomain: j;             Range: {                    {0..7}             }       }       Parameter a {             IndexDomain: (t,j);             Range: binary;       }       Variable TotalMitabeiter {             Range: free;             Definition: sum(j, x(

426
Marcel Hunting
AIMMSian
4 months ago
B
bazzaEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
Extracting list of constraints

Hi there, This might be a trivial question, but what's the easiest way of extracting a list of "active" constraints from a math program? Essentially I want the list of constraints names in the Math Program Inspector, exported into a text file. The reason behind this requirement is that I have two very similar LPs that I want to compare, to identify why they differ.I've tried: the constraints listing file (too large / complex and some formatting differences make it difficult to DIFF), exporting AllConstraints. What other options are available?Thanks! 

452
B
5 months ago
rahmat
rahmatAce
asked in Algorithmic Capabilities & Optimization Modeling
Constraint with lagged index

Dear All,In a model, I have a constraint as:y(g,t) - z(g,t) = u(g,t) - u(g,t-1) forall (g,t) All variable are binary variable. g is a set of generator unit and t is a set of time. How to implement this constraint in AIMMS if there a three generator units and the time periods (t) are 1,2, and 3. For the initial condition, generator units #1 and #2 are off-line prior to the first time period indicated by the value of u = 0 while generator unit #3 is online indicated by the value of u = 1. Thank you.

222
rahmat
5 months ago
rahmat
rahmatAce
asked in Algorithmic Capabilities & Optimization Modeling
How to perfrom complex calculation in AIMMS

Dear All,I want to perform a complex calculation in AIMMS. For example, the given data is the impedance (Z) with Z = R + iX. In a constraint, the impedance must be transferred into admittance (Y) where Y = 1/Z. Is there a method in AIMMS to do this? Thank you very much.

282
rahmat
5 months ago
A
AnneEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
Check for me the command

Hi, can you help me check this command, I want to generate the detailed infeasibility analysis report from AIMMS. How and where to declare “CPLEXParameter” and “generate InfeasibleAnalysisReport”? Is this the correct approach? if not please assist me.Thank you for your help.

305
gdiepen
AIMMS Champ
5 months ago
R
RwitamJEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
How to pass initial solution in AIMMS for an MIP/ CPLEX

I am facing runtime issues for one of my AIMMS project. I am thinking to pass an initial solution to the model before we call solve statement.  As per the documentation, I have activated the following. CPLEX X.X: Specific solvers > CPLEX X.X > General > Advanced start > Use advanced basisI have stored the initial solution in an .xlsx file. I would like to assign this value to the variable. How to do it. I am not getting the options or idea. Where to assign or how to assign if I would like to assign an initial solution to the following variable.   

523
Chris Kuip
AIMMSian
5 months ago
sarah rohaizad
sarah rohaizadEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
Unread Parameter in AIMMS

Hello, I have a question regarding AIMMS. I plan to do lab scheduling that will assign classes to a lab venue at a time. Each class will be taught by a different demonstrator, which I already specified in the parameter (Demo_Lab) as shown in the picture. However, whenever I included it in a constraint named Demo_Gap with an index domain (l,t), AIMMS did not follow the Demo_Lab parameter. AIMMS gave the results with a demonstrator randomly assigned to any class (you can refer to the final image). May I know how this is possible to happen? The parameterThe data. The demo gap constraintThe result shows AIMMS just assign demo to any classes without consider the mentioned parameter  

483
sarah rohaizad
5 months ago
sarah rohaizad
sarah rohaizadEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
Difference between Optimal solution and Found solution in AIMMS Progress

What is the difference on the program status of “Found Solution” with Optimal solution. Does “found solution” status shows the feasible result not the optimal one? Please explain.

574
sarah rohaizad
6 months ago
rahmat
rahmatAce
asked in Algorithmic Capabilities & Optimization Modeling
LP Problems with Uncertain Parameters

Dear All,I have a linear programming problem (from a book of optimization in power system) with uncertain parameters as:max z = 750x1 + 1000x2subject to:x1 + x2 <= ax1 + 2x2 <= b4x1 + 3x2 <= cx1,x2 >= 0where a, b, and c are uncertain parameters with the probability function as:How to implement this optimization problem in AIMMS?Thank you.

812
rahmat
6 months ago
R
RwitamJEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
Rake building through wagon building

Dear Team,I have a problem. I need some helps. I have several coils with weight. I have to load coils on wagons. There are two types of wagons. The capacity of two types of wagons are 64 and 67 respectively. I have to make rakes by joining wagons. There are three types of rakes. In one rake type, 1st type of wagon can be used. It takes 4 wagons to make a rake. In rake type 2, 2nd type of wagon can be used and 5 wagons are required to make a rake. If we club two different types of wagons, then also we can make rake. It takes 3 wagons to make a rake. My objective is to make full rakes and utilize all the coils with minimum cost.  I have designed a variable v_(i_Rake_Type,i_Wagon_Type,i_Wagon,i_Coil). The constraint is sum[(i_Wagon_Type,i_Wagon), v_WagonType(i_Rake_Type,'Wagon_1',i_Wagon)] = 4*sum[i_Wagon_Type, v_RakeTypeUsed(i_Rake_Type,'Wagon_1')];I am finding it sometimes problematic. In the last types of rakes, we need to use two different types of wagons. Am I doing in right way. Kin

421
T
AIMMSian
7 months ago
R
rohit2365Explorer
asked in Algorithmic Capabilities & Optimization Modeling
Indent Domain error in variable definition

I am trying to define a variable with following index domain (i, v in Vehicles_i(i),j, j1 in Nodes_J(j))I am getting a message ', )' is expected.What is the error in this definition?When I am defining as (i, v in Vehicles_i(i),j, j1)  or (i, v, j , j1 in Nodes_J(j)). It does not give any error.

281
Marcel Hunting
AIMMSian
7 months ago
R
RwitamJEnthusiast
asked in Algorithmic Capabilities & Optimization Modeling
How to write a constraint to process all the items in a box

Dear Team,I am facing one problem while writing a constraint. Let's say, I have three boxes with several items. Say box 1 has 4 items, box 2 has 6 items and box 3 has 9 items. I am processing the items day wise considering time as a constraint. I want that, if I am selecting a particular box, I will process all the items of that box 1st then will move to the next box. What I am getting that Day1-box1- 2 itemsDay1-box2-3 itemsDay1-box3-2 itemsDay2-box1-2 items.I do not want it. I want, choose a box on day 1, process all the 4 items based on the available time. I have written a constraint to handle it, which is like sum[d, v(d, boxnumber)] >= p_items(boxnumber) - v_Penalty(boxnumber)It means, I am trying to get the item number in a box while minimizing the penalty in the objective function.  Kindly help if I am doing anything wrong.

591
T
AIMMSian
7 months ago
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