Hi,
I think that the element constraint does not exactly encode your
purpose. You write:
y ? g1_reach[x] and z ? g1_reach[y] ==> z ? g1_reach[x]
while your element constraint represents something like (if I am correct)
y ? g1_reach[x] and z ? g1_reach[y] <=> z ? g1_reach[x]
i.e., this is an equivalence.
I do not know why you would have thousands of solution, though. Neither
why they do not respect the "superset" constraint.
Hope it helps anyway,
JN Monette
On 01/10/2014 10:35 AM, Tobias Pankrath wrote:
Hello,
I'm quite new to constraint programming and gecode in particular and
ran into some issue
I have to directed graphs G1=(V1,V1×V1), G2=(V2, V2×V2) and I am
searching for a mapping h: V1 ? V2, that mantains reachability. I.e.
if there is a path v1 -*> v2 (v1,v2 ? V1) than there must also be a
path h(v1) -*> h(v2).
To model this using gecode, I am using 4 SetVarArrays:
SetVarArray g1_edges; // y ? g1_edges[x]: there is an edge from v_x to
v_y in G1
SetVarArray g2_edges; // like above for G2
SetVarArray g1_reach; // y ? g1_reach[x]: there is a path from v_x to
v_y in G1
SetVarArray g2_reach; // like above for G2.
Now I want gecode to calculate the reachability of those graphs. Thus
I tried to fix the graph by the following domain constraints. A
picture of the desired graph is attached to this mail.
// define edges between nodes
dom(*this, g1_edges[0], SRT_EQ, IntSet(1, 2));
dom(*this, g1_edges[1], SRT_EQ, 5 );
dom(*this, g1_edges[2], SRT_EQ, IntSet(3,4));
dom(*this, g1_edges[3], SRT_EQ, 5);
dom(*this, g1_edges[4], SRT_EQ, 5 );
dom(*this, g1_edges[5], SRT_EQ, IntSet::empty);
Then I want to encode the following relations:
* y ? g1_reach[x], if y ? g1_edges[x] (direct neighbours)
* if y ? g1_reach[x] and z ? g1_reach[y] then z ? g1_reach[x]
(transitivity)
Thus I do:
for(int x = 0; x < 6; ++x)
{
rel(*this, g1_reach[x] >= g1_edges[x]); // superset
element(*this, g1_reach, SOT_UNION, g1_reach[x], g1_reach[x]);
// call to element taken from the manual, section 5.2.4
// is it correct?
}
Then I'll branch on g1_reach, like this:
branch(*this, g1_reach, SET_VAR_NONE(), SET_VAL_MIN_INC());
However this gives me a >1000 solutions and all look like
g1_edges {{1,2}, {5}, {3,4}, {5}, {5}, {}}
g1_reach {}
What is the correct way to model this?
With my best regards,
Tobias
_______________________________________________
Gecode users mailing list
users@gecode.org
https://www.gecode.org/mailman/listinfo/gecode-users
_______________________________________________
Gecode users mailing list
users@gecode.org
https://www.gecode.org/mailman/listinfo/gecode-users
