[gecode-users] branching...

[Martin Mann]

Hi Kilian,

inserting a branching directly into a space is very easy and doesnt need 
the wrapper function "branch".

you can do it like that in the constructor of your space:

e.g. for the integer variables

// init the variable array with your vars to branch on
// e.g. (22 vars with vals 0..9):
ints = Gecode::IntVarArray(this, 22, 0, 9);

// create a viewarray of your variables
Gecode::ViewArray<Gecode::Int::IntView>
   iv(this,(Gecode::IntVarArgs)ints);

// create the branching
new (this) Gecode::ViewValBranching<	
               Gecode::Int::IntView,
               int,
               Gecode::Int::Branch::BySizeMin,
               Gecode::Int::Branch::ValMin
             >(this, iv);
// done :)

you only have to create a new branching object with the right template 
parameters (usually done by the branch-wrapper function). the branching 
constructure itself registers to your space and thats all.

about your first question: one possibility is to generate a serie of 
branching objects:

intBranching(i1,i2)
bBranching(b1)
intBranching(i3,i4,i5,i6)
bBrachning...
...

for each you ve got to generate a viewarray of your variable-subset to 
branch on and construct a branching. you can easily write your own 
minimal wrapper function that generates these viewarrays.

hope this helps and merry christmas,

Martin


Kilian Sprotte wrote:
> Hi,
> 
> thinking about how to make gecol at least a little more flexible,
> I have some general little questions. :)
> 
> As gecol does not allow for subclassing Space
> (the SWIG CFFI wrapper creation is not really ready
> yet for c++), I am using the following hard-wired problem
> space:
> 
> class GecolSpace : public Space {
> protected:
>   IntVarArray  ints;
>   BoolVarArray bools;
>   SetVarArray  sets;
> public:
> [...]
> 
> I have seen that it is possible to call branch twice -
> for example for the ints and then for the bools, in order
> to have both of them distributed.
> 
> My first question:
> If I wanted to consider ints and bools together for branching,
> for example giving them a naive predefined, but not regular
> ordering like:
> 
> i1 i2 b1 i3 i4 i5 i6 b2 b3 i7 b4 b5 b6
> 
> Can I put them into an IntVarArgs array and treat them together?
> 
> My second question:
> If I wanted to add my own ViewSel class....
> 
> Do I actually need to change branch in branch.cc
> http://www.gecode.org/gecode-doc-latest/int_2branch_8cc-source.html#l00029 
> ?
> 
> and add my own 'case'....
> 
> Probably I can just instantiate the ViewValBranching directly?
> 
> Sorry for asking this c++ questions, I would be very grateful about a few
> words, what the necessary steps are....
> 
> Maybe it is more interesting for you what kind of custom
> distribution strategy I have in mind.
> 
> Lets say my problem has only int vars. I would like to decide the order
> of distribution according to the value (if it is already assigned) of 
> another
> var that each var points to.
> In other words, I conceptually sort my vars according to a key and
> then pick the first. There is a (fixed) mapping of each var to another
> one that serves for the key. If it is not yet assigned, we could say the
> key value was +inf.
> 
> This is actually very musically, as e.g. vars representing pitches can 
> be chosen according to their time in the score, which is represented by 
> the start time var of the chord they belong to. :)
> 
> I am keeping some good memories of the flexibility of {FD.distribute 
> +Dist +Xv} in Oz....
> For experimenting, I am hoping to provide at some point something 
> similar in Lisp,
> by using callbacks....
> 
> All of this is not so easy for a musician,
> but I need to do it :-P
> 
> Merry Xmas,
> 
>   Kilian