[gecode-users] Indexing into arrays

[Milt]

Guido,
Thanks for your quick reply!  I'd certainly missed that point about status()
...got it.
But I think I still must be missing something, because I'm getting behavior I
don't quite understand.
So I distilled my code down to the simple example below that behaves as
follows.
  -When I run the code below, I get these results (the rel(!A[0]) fails the
space):
      A[0]=1, B0=0, C=0
      A[1]=[0..1], B1=193, C=0
  -I'd have expected A[1] to be equal to 0.
  -But when I change the assignment of B0 from 
      expr(*this,0) to 
      expr(*this,192), 
   I get what I'd expect as results (the rel(!A[0]) doesn't fail the space):
      A[0]=0, B0=192, C=0
      A[1]=0, B1=193, C=0
Is this what's meant in MPG section 4.1.7, that after a space fails, the domain
may have more content than expected?

Question: If so, then when the space fails during the relation !A[0], why does
Gecode keep running my code to define A[1], do the status, and the couts?
(I'd have expected Gecode to recognize that the space failed, abandon the
failed space ASAP, and hurry to try another branching variable or value.)

Also, my approach to debugging the constraint posting within my model is to use
compiler directives (#if, #else, #endif) to maintain 2 paths thru my code: 

1 - one that is normal, branching and exploring as intended, for example on an
IntVarArray "list", which my code uses to compose constraints to post, and

2 - one that is for debugging a single test case at a time, so it branches and
updates a different variable array "list_other", which my code ignores, and
defines an IntVarArgs "list", and defines its items specifically to be a test
case I'm debugging.  So my code, which is written to examine "list", now
focuses exclusively on the test case.  This lets me avoid the confusion of the
entire design space, and see just how the test case is being treated. (e.g., why
it isn't being filtered out by the constraint I'd expect to catch it, or failing
good cases.)

Question: But, if Gecode shows extra items once it fails, as in the example
below, how can I tell when the space has failed, to know whether my code is
faulty in not narrowing down a domain, or whether some constraint has failed
for the test case and I'm getting the after-fail behavior? (and if so, is there
any simple way to detect which constraint detected the failed space, i.e., the
straw that broke the camel's back; or does order of constraint posting
matter?)

Question: Is this a reasonable debugging strategy for the constraint posting
(I'm not dealing with the search issues yet), or do people typically use other
better techniques?  (not sure where I'd look for Gecode debugging
techniques...saw your interaction w/Roberto Pinto in 2006, but I'm looking for
more of a targetable data dump of the data structures than an interactive Gist
like exploration of the design-space search order -- Gist is great, but not what
I think I need for this purpose.)

Thanks for your help,
-Milt
---------------
class Trim : public Space {
protected:
public:
        IntVarArray IVA;
        // Constructor for script
        Trim()
          :
                IVA(*this, 1, 0, 3)
                {
                IntVar B0 = expr(*this,0);
                IntVar B1 = expr(*this,193);
                int C = 0;
                BoolVarArgs A(2);
                //Post constraints
                A[0] = expr(*this,B0==C,ICL_DOM);          
                rel(*this,!A[0],ICL_DOM);
                A[1] = expr(*this,B1==C,ICL_DOM);          
                status();
                cout<<"A[0]="<<A[0]<<", B0="<<B0<<", C="<<C<<endl;
                cout<<"A[1]="<<A[1]<<", B1="<<B1<<", C="<<C<<endl;
                // post branching
                branch(*this, IVA, INT_VAR_SIZE_MIN, INT_VAL_MIN);
        }
        // search support: Constructor for cloning
        Trim(bool share, Trim& s) : Space(share, s) {
                IVA.update(*this, share, s.IVA);
        }
        // perform copying during cloning
        virtual Space* copy(bool share) {
                return new
                Trim(share,*this);
        }
};