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Adding constraints to a CPLEX model in C++


Adding constraints to a CPLEX model in C++

By : Alexis Migueres
Date : November 20 2020, 09:01 AM
To fix the issue you can do for your help, finally I could figure out what was wrong. Basically, the initialization of the variables was not correct, because I was not adding them to the model. For instance, the definition of the U variable should be as follows:
code :
typedef IloFloatVarArray NumVar1D;
typedef IloArray<IloFloatVarArray> NumVar2D;
typedef IloArray<IloArray<IloFloatVarArray> > NumVar3D;

NumVar3D U(env);
for(int i=0; i < I; i++){
    NumVar2D Ui(env);
    for(int n=0; n < N; n++){
        NumVar1D Uin(env);
        for(int r=0; r<R; r++){
            Uin.add(IloFloatVar(env));
        }
        Ui.add(Uin);
    }
    U.add(Ui);
}


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Is it possible to get different results from solving a model using CPLEX in MATLAB and CPLEX in Java?

Is it possible to get different results from solving a model using CPLEX in MATLAB and CPLEX in Java?


By : Steve G
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , Yes, absolutely. Under the hood, these languages act completely different and not just a byte code vs compiled code difference. You can write code in C code and run it through different compilers and have the results of running the code be different. If any floating point math is done, different optimizations are done by the compiler to speed up the code. Ideally a single compiler will always perform the floating point math in the same order after optimizations (so even if the code is slightly different with the same expected output, it will be the same), this assumption cannot not be held across multiple compilers/languages/hardware since floating point numbers are incredibly picky.
I haven't read this whole document, but it might be of interest to you: http://gafferongames.com/networking-for-game-programmers/floating-point-determinism/
CPLEX/OPL model - constraints with subset index

CPLEX/OPL model - constraints with subset index


By : user3585943
Date : March 29 2020, 07:55 AM
I hope this helps you . It is not clear what your problem is, but I am guessing your problem is to do with modelling things like products(j) in constraint 2. Try using sets for these - so create an array of sets of products in each product family. There are examples of this in the OPL examples provided as part of the install. For example, in the examples\opl\models\AssemblySequencing\Sequence model we have
code :
{string} computer[AllComputers] = ...;
{int} productsInFamily[prodfam] = ...;
 forall(i in blocks, j in prodfam)
   NB2: //production sub-lots
    sum(p in productsInFamily[j])q[i][p]<=y[i][j]*abs(products(j));
Adding constraints CPLEX Python API

Adding constraints CPLEX Python API


By : Carlos
Date : March 29 2020, 07:55 AM
this will help In general, you'll get better performance if you create batches of linear constraints rather than creating them one at a time. For example (using your example above), it's better to do the following:
code :
import cplex
c = cplex.Cplex()
c.variables.add(names=["x{0}".format(i+1) for i in range(9)])
c.linear_constraints.add(lin_expr=[[[0, 1, 2], [1.0, 1.0, 1.0]],
                                   [[3, 4, 5, 6], [1.0, 1.0, 1.0, 1.0]],
                                   [[7, 8], [1.0, 1.0]]],
                         rhs=[1.0, 1.0, 1.0],
                         names=["c{0}".format(i+1) for i in range(3)])
c.write("example.lp")
Minimize
 obj:
Subject To
 c1: x1 + x2 + x3  = 1
 c2: x4 + x5 + x6 + x7  = 1
 c3: x8 + x9  = 1
End
Logical constraints in CPLEX

Logical constraints in CPLEX


By : Andrew Iștoc
Date : March 29 2020, 07:55 AM
should help you out Looking at the provided OPL examples (e.g. BasketballScheduling\acc.mod) I think that the 'then' part defining the constraint should have '==' rather than '='. It is not an assignment, but declaring that the two must be equal.
CPLEX deleting constraints

CPLEX deleting constraints


By : Osama Elyas
Date : March 29 2020, 07:55 AM
To fix the issue you can do I'm calling cplex.addEq(1, x), where x is an IloIntVar, to add 1 == x as a constraint to my model cplex. , I would use delete. Let me give you a tiny example:
code :
IloCplex myCplex = new IloCplex();
IloNumVar x = myCplex.numVar(0.0, 10);
myCplex.addMinimize(x);
IloRange myConstraint = myCplex.addEq(x,1);
myCplex.add(myConstraint);
if (myCplex.solve()) 
{
  System.out.println("constraint x == 1 is active");
  System.out.println("x = " + myCplex.getValue(x));
}
myCplex.delete(myConstraint);
if (myCplex.solve()) 
{
  System.out.println("constraint x == 1 is deleted");
  System.out.println("x = " + myCplex.getValue(x));
}
  constraint x == 1 is active
  x = 1.0

  constraint x == 1 is deleted
  x = 0.0
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