Originally posted by: Ebisa

I am just starting to use the cplex optimizer, and I have this small problem to fix.
In my program, I wanted to assign a value to the first element of a dvar array. Here is the releveant part of my program:

int noOfTimesteps = ...;
range time_steps = 1 ..noOfTimesteps;
int max_storage = ...;
int min_storage = ...;
int initial_charge_level = ...;

dvar int charge_leveltime_steps in min_storage..max_storage;
charge_level[1] = initial_charge_level;

But the last line in the code is creating an error message that says "syntax error, unexpected (integer-literal)". I would appreciate if someone can help me on how to fix this. How can I assign value to the first element of the array?

Regards,
#ConstraintProgramming-General
#DecisionOptimization

Originally posted by: GGR

Hi Ebisa

To initialize arrays in a model files (apart at declaration time) you must use the script: That is your OPL code could be:

int noOfTimesteps = 10;
range time_steps = 1 ..noOfTimesteps;
int max_storage = 10;
int min_storage = 1;
int initial_charge_level = 2;
int charge_leveltime_steps;

dvar int charge_leveltime_steps in min_storage..max_storage;

// dynamic initialisation of the array charge_level
execute {
charge_level[1] = initial_charge_level;
};

Hope that helps

Note, if you want to use constraint programming, you must decalre in head of you OPL model file

using CP;

If you have an issue about OPL using constraint programing, the right forum is "OPL using CP Optimizer". If you have an issue about OPL using CPLEX Linear Programming, the right forum is "OPL using CPLEX Optimizer". Sorry for that mess but posting in a wrong forum may lead to delayed (or no) answer

Cheers
#ConstraintProgramming-General
#DecisionOptimization

Originally posted by: GGR

Hi Ebisa

Sorry, I missed charge_level is an array of variable.

To initialize a variable range you can either do it in the declaration of the array:

dvar int charge_leveli in time_steps
in ((i == 1)? initial_charge_level : min_storage)..((i==1) ? initial_charge_level : max_storage);

That is possible for not too complex cases
Either in the constraint. That is in the OPL subject to block:
subject to {
charge_level[1] == initial_charge_level;
}
Last in a script execute block:

execute {
charge_level[1].UB = initial_charge_level;
charge_level[1].LB = initial_charge_level;
}

So
for a constant to initialiie:
either in the declaration, either in a script execute block
for a variable to initialize
either in the declaration, either in a script execute block
either in the model subject to block as constraints

Cheers
#ConstraintProgramming-General
#DecisionOptimization

Originally posted by: Ebisa

Thank you for your replies,
they were helpful.

Regards
#ConstraintProgramming-General
#DecisionOptimization