{"id":33506,"date":"2023-02-09T08:50:36","date_gmt":"2023-02-09T03:20:36","guid":{"rendered":"https:\/\/jassweb.com\/solved\/solved-generating-all-triples-from-a-graph\/"},"modified":"2023-02-09T08:50:36","modified_gmt":"2023-02-09T03:20:36","slug":"solved-generating-all-triples-from-a-graph","status":"publish","type":"post","link":"https:\/\/jassweb.com\/solved\/solved-generating-all-triples-from-a-graph\/","title":{"rendered":"[Solved] Generating all triples from a graph?"},"content":{"rendered":"<p> [ad_1]<br \/>\n<\/p>\n<div id=\"answer-5610959\" class=\"answer js-answer accepted-answer js-accepted-answer\" data-answerid=\"5610959\" data-parentid=\"5594009\" data-score=\"5\" data-position-on-page=\"1\" data-highest-scored=\"1\" data-question-has-accepted-highest-score=\"1\" itemprop=\"acceptedAnswer\" itemscope itemtype=\"https:\/\/schema.org\/Answer\">\n<div class=\"post-layout\">\n<div class=\"votecell post-layout--left\"><\/div>\n<div class=\"answercell post-layout--right\">\n<div class=\"s-prose js-post-body\" itemprop=\"text\">\n<p>As discussed in the comments to the question, it&#8217;s not very clear exactly what <em>epitaph<\/em>&#8216;s setup is, and for some reason s\/he seems unwilling to clarify. But let&#8217;s suppose that the &#8220;graph&#8221; is actually simply represented by a distance matrix (which may possibly be what the mess of numbers and Xs in the question is supposed to show), with an actual numeric distance for each pair of vertices.<\/p>\n<p>In that case, there&#8217;s nothing very graph-ish going on here; there&#8217;s an edge for every pair of vertices without exception; and all we can do is to enumerate every single triple of vertices.<\/p>\n<p>For each <em>set<\/em> of three vertices a,b,c we need to check that d(a,b) &lt;= d(a,c)+d(c,b), and that d(a,c) &lt;= d(a,b)+d(b,c), and that d(b,c) &lt;= d(b,a)+d(a,c). So let&#8217;s do that. The following is pseudocode because if I try to write it in PHP (which I use as seldom as possible) I&#8217;ll make mistakes.<\/p>\n<pre><code>for i from 0 to n_vertices-3\n  for j from i+1 to n_vertices-2\n    for k from j+1 to n_vertices-1\n      # now i,j,k are three distinct vertices, and every set of three vertices\n      # will occur once as we run through the loops.\n      a = distances[i,j]\n      b = distances[i,k]\n      c = distances[j,k]\n      if a&gt;b+c or b&gt;a+c or c&gt;a+b\n        triangle inequality is violated; complain\n<\/code><\/pre>\n<p>If your graph is represented in some way other than as a distance matrix, or if lots of edges might fail to exist, then you&#8217;d want to do something different.<\/p>\n<p>(Note: if your graph is supposed to satisfy the triangle inequality, then arguably it shouldn&#8217;t be missing any edges unless it&#8217;s actually disconnected. It depends on whether the distances are intended to be &#8220;overall shortest distance from x to y&#8221; (in which case if the triangle inequality fails then something is broken, and there should be no absent edges in a connected graph) or &#8220;distance of direct path from x to y&#8221; (in which case if the triangle inequality fails it merely indicates that an allegedly direct path isn&#8217;t worth using).)<\/p>\n<\/p><\/div>\n<div class=\"mt24\"><\/div>\n<\/div>\n<p>            <span class=\"d-none\" itemprop=\"commentCount\">0<\/span> <\/p><\/div>\n<\/div>\n<p>[ad_2]<\/p>\n<p>solved Generating all triples from a graph? <\/p>\n","protected":false},"excerpt":{"rendered":"<p>[ad_1] As discussed in the comments to the question, it&#8217;s not very clear exactly what epitaph&#8216;s setup is, and for some reason s\/he seems unwilling to clarify. But let&#8217;s suppose that the &#8220;graph&#8221; is actually simply represented by a distance matrix (which may possibly be what the mess of numbers and Xs in the question &#8230; <a title=\"[Solved] Generating all triples from a graph?\" class=\"read-more\" href=\"https:\/\/jassweb.com\/solved\/solved-generating-all-triples-from-a-graph\/\" aria-label=\"More on [Solved] Generating all triples from a graph?\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[320],"tags":[457,2000,771,357,339],"class_list":["post-33506","post","type-post","status-publish","format-standard","hentry","category-solved","tag-algorithm","tag-combinatorics","tag-graph","tag-math","tag-php"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v26.5 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>[Solved] Generating all triples from a graph? - JassWeb<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/jassweb.com\/solved\/solved-generating-all-triples-from-a-graph\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"[Solved] Generating all triples from a graph? - JassWeb\" \/>\n<meta property=\"og:description\" content=\"[ad_1] As discussed in the comments to the question, it&#8217;s not very clear exactly what epitaph&#8216;s setup is, and for some reason s\/he seems unwilling to clarify. 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