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Specialised (user defined) constraints in JChoco

Specialised (user defined) constraints in JChoco. 2 examples: max and subtour elimination. Consider the following contraint. This can be implemented in JChoco using primitives as follows. Due to Chris Unsworth. Could I define my own constraint to do this? Why would I want to do that?.

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Specialised (user defined) constraints in JChoco

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  1. Specialised (user defined) constraints in JChoco 2 examples: max and subtour elimination

  2. Consider the following contraint This can be implemented in JChoco using primitives as follows

  3. Due to Chris Unsworth

  4. Could I define my own constraint to do this? Why would I want to do that? • Possibly: • more compact • faster • more propagation

  5. V[0] = max(v[1],v[2],…,v[n-1]) Define a constraint called Max that extends AbstractLargeIntConstraint

  6. Methods to be implemented V[0] = max(v[1],v[2],…,v[n-1]) initiation inf: lower bound sup: upper bound removal of value instantiate

  7. V[0] = max(v[1],v[2],…,v[n-1]) A demo Cart before the horse?

  8. V[0] = max(v[1],v[2],…,v[n-1]) Note: output always has a 4 or a 5 in it

  9. We haven’t used them yet, but …. Backtrackable Variables (Stored*)

  10. Small TSP’s

  11. The single successor model An array of n variables • “single successor” model of a graph • Limits what kind of graph can be modelled • out-degree of 1 But this aint enough

  12. The single successor model NOT A TOUR! 1 2 3 0 5 6 7 4 4 5 6 7 0 1 2 3 We need subtour elimination

  13. Yikes! Show me a picture! Associate with each variable next[i] the following reversible variables • When making an instantiation • next[i] = j • We now join the path that ends in i to path that starts with j • If the path involves less that n vertices/cities • next[e[j]] != s[i] • i.e. we cannot close that loop!

  14. 6 s[6] = 8 8 e[8] = 6 s[7] = 5 7 4 e[5] = 7 5 next[1] = 5 1 s[1] = 0 2 3 0 e[0] = 1

  15. 6 s[6] = 8 8 e[8] = 6 s[7] = 0 7 4 5 1 2 3 0 e[0] = 7

  16. 6 s[6] = 8 8 e[8] = 6 s[7] = 0 7 4 5 next[7] ≠ 0 Otherwise we have a subtour/loop This is the “propagation” . 1 2 3 0 e[0] = 7 Note: this is a constraint that may be used in a richer problem

  17. Example application: knight’s tour

  18. Wot! Show me a picture!

  19. Is there a dvo heuristic for this?

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