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12197838
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2012-08-30T13:20:51.783
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2012-08-30T13:20:51.783
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<p>I propose a solution without the suggested library or the quadtree, I stay in basic prolog (I write in SWI).</p> <p>There is actually no need for <code>assert</code>/<code>retract</code>/<code>forall</code> if I understand your problem correctly. I assume that <code>point(P)</code> says that P is the uniquely-defined reference point from which we calculate distances, but it is a bit weird (I would use it as a parameter, to ensure it is unique).</p> <pre><code>point([0,0]). % The reference point % Entry point predicate % First parameter : a list of points % Second parameter (result) : the point closest to the reference point list_min([H|Tail], Min) :- point(Reference), distance(H, Reference, D), list_min(Tail, H, D, Min). % First parameter : the list remaining to consider % Second parameter : the closest point, at this point of the computation % Third parameter : the corresponding (minimum) distance, at this point of the computation % Fourth parameter : the result (one point, to be bound at the end of computation) list_min([], CurrentMin, _, CurrentMin). % Stop condition : list processed list_min([Candidate|Tail], CurrentMin, CurrentDist, Min) :- point(Reference), distance(Candidate, Reference, CandidateDist), ( % if the new candidate is not better, keep the current candidate CurrentDist < CandidateDist -> list_min(Tail, CurrentMin, CurrentDist, Min) ; % if the new candidate is better, take it as the current candidate list_min(Tail, Candidate, CandidateDist, Min) ). distance(A,B,D):- % copy-pasted from your version A = [A1,A2], B = [B1,B2], Y is B2 - A2, X is B1 - A1, D is sqrt(X*X + Y*Y). </code></pre>
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1. POHow to return the smallest distance to a point?
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1. USEusebius
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1. POHow to return the smallest distance to a point?
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