[gecode-users] edge-finder propagator

[Filip Konvička]

Hi Jan,

> The implementation of the O(n^2) edge-finder of [Baptiste,Le Pape, 
> Nuijten] seemed to us easier to implement than the O(n log n) algorithm 
> of Vilim, which uses binary trees.
> So we chose the O(n^2), as it was the first propagator we were implementing.
> 
> Maybe we should try to implement that O(n log n) version.

The binary trees are easy - implement them using vectors: compute the 
next larger power of two (N), make a vector of N*2-1 items, the tree 
leaves start at index N-1, parent node of node I is (I-1)/2.

In fact, efficient computation of the next power of two is what I can 
share with you because it is already part of the FloatVar implementation 
I posted earlier today: it is in float/float/bi/prop_linear.icc, look 
for "namespace __Utils".

Theta-lambda trees are usable not just for propagators, but also for 
branchings (you can easily compute firsts/lasts using theta-lambda trees).

Hope this helps,
Filip