Specialised user defined constraints in JChoco

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

• Possibly
• more compact
• faster
• more propagation

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V0 max(v1,v2,,vn-1)
Define a constraint called Max that extends
AbstractLargeIntConstraint
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Methods to be implemented
V0 max(v1,v2,,vn-1)
initiation
inf lower bound sup upper bound
removal of value
instantiate
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V0 max(v1,v2,,vn-1)
A demo
Cart before the horse?
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V0 max(v1,v2,,vn-1)
Note output always has a 4 or a 5 in it
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We havent used them yet, but .
Backtrackable Variables (Stored)
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Small TSPs
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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
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The single successor model
NOT A TOUR!
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0
5
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4
7
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0
1
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We need subtour elimination
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Associate with each variable nexti the
following reversible variables

• When making an instantiation
• nexti 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
• nextej ! si
• i.e. we cannot close that loop!

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s6 8
8
e8 6
s7 5
7
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next1 5
e5 7
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s1 0
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0
e0 1
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s6 8
8
e8 6
s7 0
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5
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0
e0 7
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s6 8
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e8 6
s7 0
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next7 ? 0 Otherwise we have a
subtour/loop This is the propagation .
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0
e0 7
Note this is a constraint that may be used in a
richer problem
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Example application knights tour
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Wot! Show me a picture!
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Is there a dvo heuristic for this?
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Warnsdorff's rule
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Is there an alternative model for this?
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A knights-graph with a degree sequence 2 that is
connected i.e. adjacency matrix model of the
graph
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So?

• Jean-Francois Puget called this the glass box
• Note how this fits with AC5
• Note that we need to consider state and
  backtracking
• Why bother?

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