Hi Andrea,
What you have to do is two things, basically: 1. (as mentioned) implement a brancher yourself. 2. Information that is expensive (oe even impossible) to re-compute you should store in a subclass of Choice that you yourself can define. I think Chapter 19 (Section 19.4) is a nice example: there the brancher also does symmetry-breaking during search and it stores all symmetry information explicitly. Cheers Christian -- Christian Schulte, Professor of Computer Science, KTH, www.gecode.org/~schulte/ From: Andrea Peano [mailto:andrea.pe...@unife.it] Sent: Tuesday, September 23, 2014 2:31 PM To: Christian Schulte Cc: users@gecode.org Subject: Re: [gecode-users] Strange branching behaviour when using FunctionBrancher I'm sorry for multiple replies, but I want to ask this in a more general fashion. Consider I planned to perform a quite burdensome heuristic in a particular point of the search (that's why I'm splitting the search). Obviously this heuristics helps to prune the search space. How can I be sure that this heuristic is not recomputed more and more? Thanks, Andrea Peano On Tue, Sep 23, 2014 at 2:24 PM, Andrea Peano <andrea.pe...@unife.it> wrote: On Tue, Sep 23, 2014 at 2:09 PM, Christian Schulte <cschu...@kth.se> wrote: You can disable recomputation but this is not a good idea as it degrades performance seriously and increases memory consumption considerably. Yes, I see. What you could do (also not good) is call status() yourself. I'm already doing it, but this does not seem enough to prevent recomputation on those nodes. I call it within second_level and third_level but it's not enough. Do you mean somewhere else? The real (but tough) thing to do is to implement your own brancher. And just checking: do you know that multiple branchers are executed in the order they are created? But maybe that is not enough for you. Yes, I know, I tried to make the search as simple as possible, but there are some aspects of the problem a bit difficult to manage. Anyway, I'll find a way. Thanks for giving me a halping hand. Andrea Cheers Christian -- Christian Schulte, Professor of Computer Science, KTH, www.gecode.org/~schulte/ From: users-boun...@gecode.org [mailto:users-boun...@gecode.org] On Behalf Of Andrea Peano Sent: Tuesday, September 23, 2014 2:00 PM To: users@gecode.org Subject: Re: [gecode-users] Strange branching behaviour when using FunctionBrancher I was just reading on the Gecode guide that this behaviour is due to the "recomputation". So I have two more questions: can I completely prevent this behaviour by disabling recomputation? Has recomputation a direct effect on parallel search? Thanks, Andrea On Tue, Sep 23, 2014 at 1:22 PM, Andrea Peano <andrea.pe...@unife.it> wrote: Hello, I've implemented a search strategy by splitting the search into three levels. I think the code may explain better this strategy. void MyModel::post(Space& home) { static_cast<MyModel&>(home).second_level(); } void MyModel::second_level() { status(); //do something with the partial solution //print "second level" branch(*this, BoolBranchDirection, INT_VAL_MIN()); branch(*this, post2); } void MyModel::post2(Space& home) { static_cast<MyModel&>(home).third_level(); } void MyModel::third_level() { if(BoolBranchDirection.val()==0) { //print third level left //left branch behaviour (install further branches) } else { //print third level right //right branch behaviour (install further branches) } } Imagine now we are fixing the partial solution before the "post" calling, so the solver goes only once into the "post" function (and it's confirmed by GIST). The strange fact is that "second_level" is called more than once! Instead I expect one call for "second_level" and two calls for "third_level", which executes two different paths of the code. These are the prints I read: second level third level left second level third level right second level third level right But I expected: second level third level left third level right Can you clarify this behaviour please? Furthermore, I experienced that I need to call "status()" within the second level, to ground some variables I expected to be already ground. Is this normal? I'm using Gecode 4.2.1 Thanks, Andrea -- Andrea Peano - PhD student Department of Engineering - University of Ferrara Tel: +39 0532 97 4827 -- Andrea Peano - PhD student Department of Engineering - University of Ferrara Tel: +39 0532 97 4827 -- Andrea Peano - PhD student Department of Engineering - University of Ferrara Tel: +39 0532 97 4827 -- Andrea Peano - PhD student Department of Engineering - University of Ferrara Tel: +39 0532 97 4827
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