[gecode-users] Attempt to invoke operation on failed space?

[Peter Tiedemann]

Thank you for taking the time to answer.

On 18/04/07, Mikael Zayenz Lagerkvist <zayenz at gmail.com> wrote:
> When the search-procedure recomputes a node, it will not follow
> exactly the same path as the first time - several branching decisions
> are added at once and then a fixpoint is computed (this is called
> batch recomputation). If this fails, the an error such as the one you
> observed might be thrown. This is one potential cause for your
> problem.

If i turn off re-computation i no longer suffer this problem, so this
could very well be the source of my problem.

> One of the key properties that Gecode uses for enabling batch
> recomputation this is that propagators should be monotonic. Typical
> cases where propagators are non-monotonic might be: not subscribing to
> all events used, using heuristic/random propagation algorithms,
> reporting ES_FIX when that is not the case, and of course general
> bugs.

I think what i am working on fits nicely into the category of
heuristic propagation. The propagator in question is not generally
monotonic (ie it might detect in-feasibility on one set of domains and
neglect to spot in-feasibility of a stricter set of domains) and in
addition the result of assign, propagate, assign,propagate and
assign,assign, propagate, propagate is not guaranteed to be the same.
Propagation is however completely deterministic.

So i guess this should be the source of my problem, right?

I suppose i will just have to run without re-computation.

Thank your for explaining this. The propagator im working with is a
bit 'special' so i suppose it isn't too surprising that im
encountering this type of issue :)

Peter Tiedemann