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POPerformance issues on prolog
 

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    <p>I'm currently implementing an prolog program to calculate the shortest path between two points. The framework exists already in a Java project. As a requirement the path must be implemented in prolog. Therefore I use gnu.prolog (<a href="http://www.gnu.org/software/gnuprologjava/" rel="nofollow">http://www.gnu.org/software/gnuprologjava/</a>)</p> <p>Out of java I call <code>searchPath(1,5,Path)</code> which will return <code>Path=[5,4,3,2,1]</code></p> <p>Here is my prolog code:</p> <pre><code>:- dynamic(path/3). findPath( [Goal | Rest], Goal, Temp, Temp, [Goal | Rest]). findPath( [A | Rest], Goal, Cost, Temp, Path) :- path(A,B,C), \+member(B, [A | Rest]), NewCosts is (Temp + C), findPath([B, A | Rest], Goal, Cost, NewCosts, Path). searchPath(Start,Goal,Path_to_goal) :- findPath([Start], Goal, Cost1, 0, Path), findPath([Start], Goal, Cost2, 0, Path2), Cost1=&lt;Cost2, Path_to_goal = Path. </code></pre> <p>I have two issues with that:</p> <ol> <li><p>The <code>searchPath</code> method <strong>should return the shortest path</strong>. However it does <strong>NOT</strong>. This results in the fact that my ghost "decides" to switch direction at some point resulting in the ghost jittering from left to right.</p></li> <li><p>My prolog code takes up to <strong>6 seconds</strong> to return a result. I don't have to tell you that this is far too much time. However sometimes prolog only needs <strong>19ms</strong>. I wasn't able to figure out on which circumstances this depends on. For example a path list containing 99 elements takes 19ms to calculate but the 6 seconds were spent on a list containing only 38 elements.</p></li> </ol> <p>Can you suggest any improvements?</p> <p>Thanks for your help in advance!</p>
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