Re: Defining a variable of mixed datatype in Mathprog

[Mate Hegyhati]

Hi!

I'd assume, that the language does not support something like this. 
Others will tell if I'm wrong.

I don't know your special use-case, but I'd generally speak against such 
a practice. It seems cleaner if one knows whether a variable is integer 
or not.

However, if this would make the rest of the model cleaner, and it is 
more important than efficiency, you can always do this:

set intset;
set contset;

set all := intset union contset;

var intvar {intset} integer;
var mixedvar {all} >=0;

s.t. foobar{i in intset}:
  intvar[i] = mixedvar[i];

I thought that the presolver would maybe kick in and remove the 
unnecessary variables, but it doesn't seem to do so. (v4.65)
I haven't tried commercial solvers, but I'd assume they do.

All the best!

Mate



On 2022. 03. 15. 7:26, Anku Pandey wrote:
> Hi,
>
> I have to formulate a problem in mathprog where a variable can be both 
> integer type and continuous type based on index.
>
> Let me give an example to further illustrate this.
>
> I have two sets of items:
> set itemInteger;
> set itemContinuous;
>
> I need to define a variable, awardQuantity, on these sets so that for 
> items in the set itemInteger, it is of type Integer and for items in set 
> itemContinuous, it is of type continuous.
>
> I know I can define two different variables:
>
> var awardQuantityInt[i in itemInteger], integer;
> var awardQuantityCont[i in itemContinuous];
>
> But that is not what I am looking for.
> I want a single variable handling both types.
>
>
>
> I would really appreciate it if I can get some help on it. I have been 
> trying to find an answer to this for a few days now.
>
> Thanks,
> Anku