Re: [Help-glpk] Even integer numbers

[Kevin Hunter Kesling]

At 7:31am -0400 Wed, 01 Oct 2014, Zvonko Bregar wrote:
> Hi everybody,
> Does there exist an expression
> That forces
> An integer variable X \in { 1, 2, 3, ...}
> To take the values only from even numbers
> X \in {2, 4, 6, ...}

I'm a bit late to this party, but it seems to me you only need a single 
second integer variable.  That is, the definition of an even number is 
one that is twice another integer.[1]  In mathematical form:

  even_number = 2 * any_integer

In mathematical optimization then, you can just use a second integer 
variable and constraint:

    X and Y are general integers
    X = 2*Y

If you need it constrained further (e.g., greater than 0 as you 
specified in your question), it's your choice how to do that.  Any of 
these would work to satisfy your question's example lower bound, and 
more than one would be overkill/wasted computing time:

    X >= 1
    X >= 2
    Y >= 1

I'd assume GLPK can handle this just fine.

Kevin

[1] Wolfram can expound much more eloquently than I: 
http://mathworld.wolfram.com/EvenNumber.html