{"id":4970,"date":"2023-12-15T12:36:56","date_gmt":"2023-12-15T11:36:56","guid":{"rendered":"https:\/\/erlebnisland-mathematik.de\/?page_id=4970"},"modified":"2024-01-03T13:35:26","modified_gmt":"2024-01-03T12:35:26","slug":"advanced-text-round-trips-through-saxony","status":"publish","type":"page","link":"https:\/\/erlebnisland-mathematik.de\/en\/advanced-text-round-trips-through-saxony\/","title":{"rendered":"Round trips through Saxony"},"content":{"rendered":"<div class=\"wpb-content-wrapper\"><p>[vc_row drowwidth=&#8221;sidebar-biest-default sidebar-biest&#8221;][vc_column][vc_column_text]<\/p>\n<h1>Round trips through Saxony<\/h1>\n<p> Imagine you are planning a round trip through the largest cities in Saxony. You only want to visit each city once and the round trip should be as short as possible. The &#8220;Round trip through Saxony&#8221; exhibit allows you to plan your journey as efficiently as possible.<\/p>\n<p>[\/vc_column_text][vc_single_image image=&#8221;4933&#8243; img_size=&#8221;large&#8221; alignment=&#8221;center&#8221;]Figure 1: The exhibit[\/vc_single_image][vc_column_text]<\/p>\n<h3>And now &#8230; the mathematics:<\/h3>\n<p>[\/vc_column_text][vc_column_text]Such a problem is also called the <a href=\"https:\/\/erlebnisland-mathematik.de\/en\/advanced-text-eulers-lines\/\">&#8220;<\/a><em><a href=\"https:\/\/en.wikipedia.org\/wiki\/Travelling_salesman_problem\">Traveling Salesmen Problem<\/a><a href=\"https:\/\/erlebnisland-mathematik.de\/en\/advanced-text-eulers-lines\/\">&#8220;<\/a><\/em> (TSP)<em>.<\/em> This can be modeled using <a href=\"https:\/\/en.wikipedia.org\/wiki\/Graph_(discrete_mathematics)\">graphs<\/a>. An (undirected) graph is an entity that consists of vertices and edges. Each edge connects two vertices (cf. [1]). For example, the &#8220;House of St Nicholas&#8221; is a graph consisting of 5 corners and 8 edges (see also the exhibit <a href=\"https:\/\/erlebnisland-mathematik.de\/en\/advanced-text-eulers-lines\/\">&#8220;Euler&#8217;s lines&#8221;<\/a>).[\/vc_column_text][vc_single_image image=&#8221;4945&#8243; img_size=&#8221;medium&#8221; alignment=&#8221;center&#8221;]Abbildung 2: House of St Nicholas[\/vc_single_image][vc_column_text]<\/p>\n<div>\u00a0In mathematics, we write this as follows: A graph <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-b3054a13ddb8dcaae20c7806ee8ed613_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#40;&#86;&#44;&#69;&#41;\" title=\"Rendered by QuickLaTeX.com\" height=\"19\" width=\"47\" style=\"vertical-align: -5px;\"\/> consists of<\/div>\n<ul>\n<li>a finite set <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-bbc70ec0280e29848d9e06a28b607e78_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#86;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"13\" style=\"vertical-align: 0px;\"\/> of <em>vertices<\/em>,<\/li>\n<li>a set <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-0dbac3854bb1ff4a1f8dc25da227cefa_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#69;&#32;&#92;&#115;&#117;&#98;&#115;&#101;&#116;&#101;&#113;&#32;&#92;&#123;&#32;&#92;&#123;&#105;&#44;&#106;&#92;&#125;&#32;&#92;&#99;&#111;&#108;&#111;&#110;&#32;&#105;&#44;&#106;&#32;&#92;&#105;&#110;&#32;&#86;&#32;&#92;&#125;\" title=\"Rendered by QuickLaTeX.com\" height=\"19\" width=\"159\" style=\"vertical-align: -5px;\"\/> of <em>edges<\/em>.<\/li>\n<\/ul>\n<p>[\/vc_column_text][vc_single_image image=&#8221;4937&#8243; img_size=&#8221;medium&#8221; alignment=&#8221;center&#8221;]Abbildung 3: Example of a graph[\/vc_single_image][vc_column_text]In addition, we assign each edge <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-ef792ea87c9b40db42ffabf9da4fbb57_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#92;&#123;&#105;&#44;&#106;&#92;&#125;&#32;&#92;&#105;&#110;&#32;&#69;\" title=\"Rendered by QuickLaTeX.com\" height=\"19\" width=\"72\" style=\"vertical-align: -5px;\"\/> a quantity <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-289df0505266766ff03bc917ef90b6a6_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#99;&#95;&#123;&#105;&#106;&#125;&#32;&#92;&#103;&#101;&#113;&#32;&#48;\" title=\"Rendered by QuickLaTeX.com\" height=\"18\" width=\"48\" style=\"vertical-align: -6px;\"\/>, the so-called <em>edge weight<\/em>. This can be interpreted, for example, as a geographical length, as the time required to travel from <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-6bcb0de135c476d4cc7796bd7ee97d13_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#105;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"5\" style=\"vertical-align: 0px;\"\/> to <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-d5ea7b6edb00cfc61a31e301837e9185_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#106;\" title=\"Rendered by QuickLaTeX.com\" height=\"16\" width=\"8\" style=\"vertical-align: -4px;\"\/> or as the cost of a journey.<\/p>\n<div>Figure 2 shows a graph whose corner set consists of the corners <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-356ccb0884df7a9a69cbfa4ae397fc49_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#65;&#44;&#66;&#44;&#67;&#44;&#68;&#44;&#69;\" title=\"Rendered by QuickLaTeX.com\" height=\"16\" width=\"97\" style=\"vertical-align: -3px;\"\/> and which has the edge set<\/div>\n<div>\n<p class=\"ql-center-displayed-equation\" style=\"line-height: 19px;\"><span class=\"ql-right-eqno\"> &nbsp; <\/span><span class=\"ql-left-eqno\"> &nbsp; <\/span><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-0b861816d6ca3e1e96a3c0fb9b5acfea_l3.png\" height=\"19\" width=\"647\" class=\"ql-img-displayed-equation quicklatex-auto-format\" alt=\"&#92;&#98;&#101;&#103;&#105;&#110;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;&#69;&#32;&#61;&#32;&#92;&#123;&#32;&#92;&#123;&#65;&#44;&#66;&#92;&#125;&#44;&#32;&#92;&#123;&#65;&#44;&#68;&#92;&#125;&#44;&#32;&#92;&#123;&#67;&#44;&#65;&#92;&#125;&#44;&#32;&#92;&#123;&#66;&#44;&#69;&#92;&#125;&#44;&#32;&#92;&#123;&#66;&#44;&#68;&#92;&#125;&#44;&#32;&#92;&#123;&#66;&#44;&#67;&#92;&#125;&#44;&#32;&#92;&#123;&#67;&#44;&#68;&#92;&#125;&#44;&#32;&#92;&#123;&#67;&#44;&#69;&#92;&#125;&#44;&#32;&#92;&#123;&#68;&#44;&#69;&#92;&#125;&#44;&#32;&#92;&#123;&#69;&#44;&#65;&#92;&#125;&#32;&#92;&#125;&#46;&#92;&#101;&#110;&#100;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;\" title=\"Rendered by QuickLaTeX.com\"\/><\/p>\n<\/div>\n<div><\/div>\n<div>Here, particularly, we do not distinguish the edges <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-8ae8c7771495ef7492c16280f11ce1df_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#92;&#123;&#65;&#44;&#66;&#92;&#125;\" title=\"Rendered by QuickLaTeX.com\" height=\"19\" width=\"49\" style=\"vertical-align: -5px;\"\/> and <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-a7ae5568d92fb55a15697b5de457d0c4_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#92;&#123;&#66;&#44;&#65;&#92;&#125;\" title=\"Rendered by QuickLaTeX.com\" height=\"19\" width=\"49\" style=\"vertical-align: -5px;\"\/>, since <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-7bc4878309687a2fa85df693d9e4b386_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#99;&#95;&#123;&#65;&#66;&#125;&#32;&#61;&#32;&#52;&#32;&#61;&#32;&#99;&#95;&#123;&#66;&#65;&#125;\" title=\"Rendered by QuickLaTeX.com\" height=\"15\" width=\"109\" style=\"vertical-align: -3px;\"\/> coincides. A graph with this property is also referred to as an <em>undirected graph<\/em>. In particular, the edge weights fulfill the <em>triangle inequality<\/em>, i.e. the distance between two vertices <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-6bcb0de135c476d4cc7796bd7ee97d13_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#105;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"5\" style=\"vertical-align: 0px;\"\/> and <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-d5ea7b6edb00cfc61a31e301837e9185_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#106;\" title=\"Rendered by QuickLaTeX.com\" height=\"16\" width=\"8\" style=\"vertical-align: -4px;\"\/>, for example, is smaller than the distance from <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-6bcb0de135c476d4cc7796bd7ee97d13_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#105;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"5\" style=\"vertical-align: 0px;\"\/> to <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-a0c053c7b75e01ffaa827a371eebe37d_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#107;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"9\" style=\"vertical-align: 0px;\"\/> plus the distance from <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-a0c053c7b75e01ffaa827a371eebe37d_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#107;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"9\" style=\"vertical-align: 0px;\"\/> to <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-d5ea7b6edb00cfc61a31e301837e9185_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#106;\" title=\"Rendered by QuickLaTeX.com\" height=\"16\" width=\"8\" style=\"vertical-align: -4px;\"\/>. In general, this can be written for any vertices <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-280ff2fe3df983aa5d27b9cc4a7844f2_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#105;&#44;&#106;&#44;&#107;&#32;&#92;&#105;&#110;&#32;&#86;\" title=\"Rendered by QuickLaTeX.com\" height=\"17\" width=\"74\" style=\"vertical-align: -4px;\"\/> as follows<\/div>\n<div>\n<div>\n<p class=\"ql-center-displayed-equation\" style=\"line-height: 17px;\"><span class=\"ql-right-eqno\"> &nbsp; <\/span><span class=\"ql-left-eqno\"> &nbsp; <\/span><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-a547b21af50e4a686e4dda60842b23ce_l3.png\" height=\"17\" width=\"105\" class=\"ql-img-displayed-equation quicklatex-auto-format\" alt=\"&#92;&#98;&#101;&#103;&#105;&#110;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;&#99;&#95;&#123;&#105;&#106;&#125;&#32;&#92;&#108;&#101;&#113;&#32;&#99;&#95;&#123;&#105;&#107;&#125;&#32;&#43;&#32;&#99;&#95;&#123;&#107;&#106;&#125;&#46;&#92;&#101;&#110;&#100;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;\" title=\"Rendered by QuickLaTeX.com\"\/><\/p>\n<\/div>\n<div><\/div>\n<div>The aim of a TSP is now to find the shortest <em>tour<\/em>\u00a0(also called <a href=\"https:\/\/en.wikipedia.org\/wiki\/Hamiltonian_path_problem\"><em>Hamilton circle<\/em><\/a>) in the underlying graph, i.e. a round trip in which we visit each city only once and end in the city in which we started our journey. A tour is also called a circle in the graph, although it does not have to be circular. In Figure 3, for example, the red-coloured edges form a tour in this graph. Its length is then calculated by adding the edge weights, i.e. the length of this tour is [\/vc_column_text][vc_column_text]<\/div>\n<\/div>\n<div>\n<p class=\"ql-center-displayed-equation\" style=\"line-height: 14px;\"><span class=\"ql-right-eqno\"> &nbsp; <\/span><span class=\"ql-left-eqno\"> &nbsp; <\/span><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-6508b3d3d054f6b408e91ab301868cd1_l3.png\" height=\"14\" width=\"270\" class=\"ql-img-displayed-equation quicklatex-auto-format\" alt=\"&#92;&#98;&#101;&#103;&#105;&#110;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;&#99;&#95;&#123;&#65;&#66;&#125;&#32;&#43;&#32;&#99;&#95;&#123;&#66;&#67;&#125;&#32;&#43;&#32;&#99;&#95;&#123;&#67;&#68;&#125;&#32;&#43;&#32;&#99;&#95;&#123;&#68;&#69;&#125;&#32;&#43;&#32;&#99;&#95;&#123;&#69;&#65;&#125;&#32;&#61;&#32;&#49;&#56;&#46;&#92;&#101;&#110;&#100;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;\" title=\"Rendered by QuickLaTeX.com\"\/><\/p>\n<\/div>\n<div>\n<p>However, there is a tour that is even shorter. Can you find it?[\/vc_column_text][vc_column_text]<\/p>\n<\/div>\n<div>\n<h4>Modelling the exhibit as a graph<\/h4>\n<div>\n<p>[\/vc_column_text][vc_column_text]The graph modelling our exhibit has the corner set<\/p>\n<p class=\"ql-center-displayed-equation\" style=\"line-height: 72px;\"><span class=\"ql-right-eqno\"> &nbsp; <\/span><span class=\"ql-left-eqno\"> &nbsp; <\/span><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-f432187332ba4f9d1301015e128f453a_l3.png\" height=\"72\" width=\"650\" class=\"ql-img-displayed-equation quicklatex-auto-format\" alt=\"&#92;&#98;&#101;&#103;&#105;&#110;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;&#86;&#32;&#61;&#32;&#92;&#32;&#38;&#92;&#123;&#92;&#116;&#101;&#120;&#116;&#123;&#68;&#114;&#101;&#115;&#100;&#101;&#110;&#44;&#32;&#76;&#101;&#105;&#112;&#122;&#105;&#103;&#44;&#32;&#67;&#104;&#101;&#109;&#110;&#105;&#116;&#122;&#44;&#32;&#83;&#99;&#104;&#107;&#101;&#117;&#100;&#105;&#116;&#122;&#125;&#44;&#32;&#92;&#116;&#101;&#120;&#116;&#123;&#32;&#69;&#105;&#108;&#101;&#110;&#98;&#117;&#114;&#103;&#44;&#32;&#87;&#117;&#114;&#122;&#101;&#110;&#44;&#32;&#84;&#111;&#114;&#103;&#97;&#117;&#44;&#32;&#68;&ouml;&#98;&#101;&#108;&#110;&#125;&#44;&#32;&#92;&#92;&#32;&#38;&#92;&#116;&#101;&#120;&#116;&#123;&#80;&#108;&#97;&#117;&#101;&#110;&#44;&#32;&#90;&#119;&#105;&#99;&#107;&#97;&#117;&#44;&#32;&#65;&#117;&#101;&#44;&#32;&#65;&#110;&#110;&#97;&#98;&#101;&#114;&#103;&#45;&#66;&#117;&#99;&#104;&#104;&#111;&#108;&#122;&#44;&#32;&#70;&#114;&#101;&#105;&#98;&#101;&#114;&#103;&#44;&#32;&#70;&#114;&#101;&#105;&#116;&#97;&#108;&#44;&#32;&#80;&#105;&#114;&#110;&#97;&#44;&#32;&#125;&#32;&#92;&#92;&#32;&#38;&#92;&#116;&#101;&#120;&#116;&#123;&#77;&#101;&#105;&#115;&#115;&#101;&#110;&#44;&#32;&#66;&#97;&#117;&#116;&#122;&#101;&#110;&#44;&#32;&#75;&#97;&#109;&#101;&#110;&#122;&#44;&#32;&#125;&#32;&#92;&#116;&#101;&#120;&#116;&#123;&#72;&#111;&#121;&#101;&#114;&#115;&#119;&#101;&#114;&#100;&#97;&#44;&#32;&#71;&ouml;&#114;&#108;&#105;&#116;&#122;&#44;&#32;&#90;&#105;&#116;&#116;&#97;&#117;&#125;&#32;&#92;&#125;&#46;&#92;&#101;&#110;&#100;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;\" title=\"Rendered by QuickLaTeX.com\"\/><\/p>\n<p>It therefore consists of a total of 21 different cities, each of which represents a corner in our graph. The set of edges results from the choice of route through the cities of Saxony. For example, if we start our journey in Dresden and want to travel from there to Leipzig first, then this route would correspond to the edge<\/p>\n<p class=\"ql-center-displayed-equation\" style=\"line-height: 19px;\"><span class=\"ql-right-eqno\"> &nbsp; <\/span><span class=\"ql-left-eqno\"> &nbsp; <\/span><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-7deeda71e777837e4a0c4a4b4d075f41_l3.png\" height=\"19\" width=\"222\" class=\"ql-img-displayed-equation quicklatex-auto-format\" alt=\"&#92;&#98;&#101;&#103;&#105;&#110;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;&#117;&#32;&#92;&#99;&#111;&#108;&#111;&#110;&#101;&#113;&#113;&#32;&#92;&#123;&#32;&#92;&#116;&#101;&#120;&#116;&#123;&#68;&#114;&#101;&#115;&#100;&#101;&#110;&#44;&#32;&#76;&#101;&#105;&#112;&#122;&#105;&#103;&#125;&#32;&#92;&#125;&#32;&#92;&#105;&#110;&#32;&#69;&#46;&#92;&#101;&#110;&#100;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;\" title=\"Rendered by QuickLaTeX.com\"\/><\/p>\n<div>The edge weight <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-2a2291f5f5d0db31ee5a92466a5181c4_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#99;&#95;&#123;&#68;&#114;&#101;&#115;&#100;&#101;&#110;&#44;&#32;&#76;&#101;&#105;&#112;&#122;&#105;&#103;&#125;\" title=\"Rendered by QuickLaTeX.com\" height=\"14\" width=\"98\" style=\"vertical-align: -6px;\"\/> is the geographical distance between Dresden and Leipzig (&#8220;as the crow flies&#8221;).<\/div>\n<div><\/div>\n<div>Perhaps you were able to quickly determine the shortest route in the graph in Figure 2. However, as you will soon realise, this task is not so easy with this exhibit. This is because you have a total of<\/div>\n<div>\n<p class=\"ql-center-displayed-equation\" style=\"line-height: 38px;\"><span class=\"ql-right-eqno\"> &nbsp; <\/span><span class=\"ql-left-eqno\"> &nbsp; <\/span><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-aeb8926f2c59a04ceabbc19a2e81243b_l3.png\" height=\"38\" width=\"236\" class=\"ql-img-displayed-equation quicklatex-auto-format\" alt=\"&#92;&#98;&#101;&#103;&#105;&#110;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;&#92;&#102;&#114;&#97;&#99;&#123;&#50;&#48;&#33;&#125;&#123;&#50;&#125;&#32;&#61;&#32;&#49;&#32;&#92;&#44;&#32;&#50;&#49;&#54;&#32;&#92;&#44;&#32;&#52;&#53;&#49;&#32;&#92;&#44;&#32;&#48;&#48;&#52;&#32;&#92;&#44;&#32;&#48;&#56;&#56;&#32;&#92;&#44;&#32;&#51;&#50;&#48;&#32;&#92;&#44;&#32;&#48;&#48;&#48;&#92;&#101;&#110;&#100;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;\" title=\"Rendered by QuickLaTeX.com\"\/><\/p>\n<\/div>\n<div>(i.e. over a trillion!) different tours available. Incidentally, the number of possible routes in the graph in Figure 2 is <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-c60cda715053a03a8c74c649d67911f7_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#49;&#50;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"16\" style=\"vertical-align: 0px;\"\/>. As you can see, this number can increase significantly with a large number of corners. We will explain why this is the case in the next section.<\/div>\n<p>[\/vc_column_text][vc_column_text]<\/p>\n<\/div>\n<div>\n<h4>P versus NP<\/h4>\n<p>[\/vc_column_text][vc_column_text]Let&#8217;s assume we want to visit <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-8ad02d5f0d297c7adacb6b8c4f9fee74_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;\" title=\"Rendered by QuickLaTeX.com\" height=\"8\" width=\"8\" style=\"vertical-align: 0px;\"\/> (<img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-695b2711f60f4d9d8e8fb9184a739f42_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;&#32;&#62;&#32;&#50;\" title=\"Rendered by QuickLaTeX.com\" height=\"14\" width=\"40\" style=\"vertical-align: -2px;\"\/>) cities and we are already in one of these cities. From our starting point, we have exactly <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-e7a7cc9c3c159f61e726d218b7300aaa_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;&#32;&#45;&#32;&#49;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"38\" style=\"vertical-align: 0px;\"\/> other cities to choose from as our next destination. After choosing the second destination, we now have exactly <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-a039b2fd5638590fd03be5441556d6ae_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;&#32;&#45;&#32;&#50;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"38\" style=\"vertical-align: 0px;\"\/> other cities to choose from for the third city, and so on. Combinatorially, we could say that we have an urn model without putting back, whereby we attach importance to the order. If we continue like this, we will have visited all <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-8ad02d5f0d297c7adacb6b8c4f9fee74_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;\" title=\"Rendered by QuickLaTeX.com\" height=\"8\" width=\"8\" style=\"vertical-align: 0px;\"\/> cities at some point. There is exactly one more station left, namely to return to our starting city. This results in an <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-b6da62038a7586c1b1eb29c2c339ef88_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;&#32;&#43;&#32;&#49;\" title=\"Rendered by QuickLaTeX.com\" height=\"14\" width=\"38\" style=\"vertical-align: -2px;\"\/> step <a href=\"https:\/\/www.mindmanager.com\/en\/features\/tree-diagram\/\"><em>tree diagram<\/em><\/a>.[\/vc_column_text][vc_single_image image=&#8221;4949&#8243; img_size=&#8221;medium&#8221; alignment=&#8221;center&#8221;]Abbildung 4: {Tree diagram for <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-a53b9b5c2a167bc471c6a43cc01a9b01_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;&#32;&#61;&#32;&#52;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"41\" style=\"vertical-align: 0px;\"\/>[\/vc_single_image][vc_column_text]Figure 4 shows this for the case <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-a53b9b5c2a167bc471c6a43cc01a9b01_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;&#32;&#61;&#32;&#52;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"41\" style=\"vertical-align: 0px;\"\/>. Here you can also see that all routes occur twice, depending on the direction in which the tour is run (clockwise or anti-clockwise). For example, the tour <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-644a752b45360b93a948379dddb07a0c_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#49;&#32;&#45;&#32;&#50;&#32;&#45;&#32;&#51;&#32;&#45;&#32;&#52;&#32;&#45;&#32;&#49;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"129\" style=\"vertical-align: 0px;\"\/> is the same as <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-7802d4b5a618001702412d5e4a1f519e_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#49;&#32;&#45;&#32;&#52;&#32;&#45;&#32;&#51;&#32;&#45;&#32;&#50;&#32;&#45;&#32;&#49;\" title=\"Rendered by QuickLaTeX.com\" height=\"12\" width=\"129\" style=\"vertical-align: 0px;\"\/>. There are therefore a total of<\/p>\n<p class=\"ql-center-displayed-equation\" style=\"line-height: 39px;\"><span class=\"ql-right-eqno\"> (1) <\/span><span class=\"ql-left-eqno\"> &nbsp; <\/span><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-d090c6c9305e1ed458f740c421eb6d4c_l3.png\" height=\"39\" width=\"265\" class=\"ql-img-displayed-equation quicklatex-auto-format\" alt=\"&#92;&#98;&#101;&#103;&#105;&#110;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;&#92;&#102;&#114;&#97;&#99;&#123;&#49;&#125;&#123;&#50;&#125;&#32;&#92;&#99;&#100;&#111;&#116;&#32;&#40;&#110;&#32;&#45;&#32;&#49;&#41;&#32;&#92;&#99;&#100;&#111;&#116;&#32;&#40;&#110;&#32;&#45;&#32;&#50;&#41;&#32;&#92;&#99;&#100;&#111;&#116;&#115;&#32;&#49;&#32;&#61;&#32;&#92;&#102;&#114;&#97;&#99;&#123;&#40;&#110;&#32;&#45;&#32;&#49;&#41;&#33;&#125;&#123;&#50;&#125;&#32;&#92;&#101;&#110;&#100;&#123;&#97;&#108;&#105;&#103;&#110;&#42;&#125;\" title=\"Rendered by QuickLaTeX.com\"\/><\/p>\n<p>possible different tours available, where we multiply by <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-cb20a9d394e4ec98a36796eeb0124cd0_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#92;&#102;&#114;&#97;&#99;&#123;&#49;&#125;&#123;&#50;&#125;\" title=\"Rendered by QuickLaTeX.com\" height=\"22\" width=\"7\" style=\"vertical-align: -6px;\"\/> because, as just noted, each tour occurs twice. Incidentally, the number can also be obtained by counting and halving the number of all paths in the tree diagram.<\/p>\n<div><\/div>\n<div>\n<p>If you now want to use a computer to determine the shortest tour, it would have to calculate every single tour and select the shortest one from all these tours. For large <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-8ad02d5f0d297c7adacb6b8c4f9fee74_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#110;\" title=\"Rendered by QuickLaTeX.com\" height=\"8\" width=\"8\" style=\"vertical-align: 0px;\"\/> this is no longer &#8220;efficient&#8221; and would take too long (certainly longer than a human life). According to (1), the number of calculation steps required for this even increases more than exponentially with the number of cities. However, it can always be decided quickly whether a selected edge set is also a tour in the graph, because a computer would only have to check whether we have ended our journey where we started it and whether every other city has only been visited once. This task can therefore be decided &#8220;efficiently&#8221; or in <a href=\"https:\/\/en.wikipedia.org\/wiki\/Time_complexity#Polynomial_time\">&#8220;polynomial time&#8221;<\/a> by a computer, i.e. the number of calculation steps to check the correctness of a route depends at most polynomially on the number of corners. A possible, but not optimal, route can be seen in Figure 2.<\/p>\n<\/div>\n<p>[\/vc_column_text][vc_single_image image=&#8221;4953&#8243; img_size=&#8221;large&#8221; alignment=&#8221;center&#8221;]Abbildung 5: A possible, but not optimal, solution for the TSP[\/vc_single_image][vc_column_text]<\/p>\n<p>There is also a scale on the exhibit that shows you how short your tour is compared to the optimum tour.<\/p>\n<div>It is also said that the travelling salesman problem is in the <a href=\"https:\/\/en.wikipedia.org\/wiki\/NP_(complexity)\">complexity class <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-2475fabae3aa136d5542f11ad3fa0acd_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#78;&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"25\" style=\"vertical-align: 0px;\"\/><\/a> (non-deterministic polynomial) and the <a href=\"https:\/\/en.wikipedia.org\/wiki\/Entscheidungsproblem\">decision problem,<\/a> which determines whether a selected edge set is a tour, is in the <a href=\"https:\/\/en.wikipedia.org\/wiki\/P_(complexity)\">complexity class <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-abc95366fcad467cee6b50cb061004c3_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"12\" style=\"vertical-align: 0px;\"\/><\/a> (polynomial). An unsolved problem to date is whether <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-6b4c9c5e099642138bf542d978d328b7_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#78;&#80;&#32;&#61;&#32;&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"61\" style=\"vertical-align: 0px;\"\/> holds, i.e. whether the class <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-abc95366fcad467cee6b50cb061004c3_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"12\" style=\"vertical-align: 0px;\"\/> of all problems that can be solved in polynomial time is equal to the class <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-2475fabae3aa136d5542f11ad3fa0acd_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#78;&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"25\" style=\"vertical-align: 0px;\"\/> of all problems for which a proposed solution can be checked for correctness in polynomial time. This problem is one of the seven <em><a href=\"https:\/\/en.wikipedia.org\/wiki\/Millennium_Prize_Problems\">Millennium Prize Problems<\/a><\/em>, of which only the <a href=\"https:\/\/en.wikipedia.org\/wiki\/Poincar\u00e9_conjecture\">Poincar\u00e9 conjecture<\/a> was proved by Grigori Perelmann in 2002. In order to solve the <em><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-b96195cbb695083f95874f351090f15c_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#80;&#45;&#78;&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"59\" style=\"vertical-align: 0px;\"\/> problem<\/em>, one would have to find an algorithm that can solve a problem from the complexity class <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-2475fabae3aa136d5542f11ad3fa0acd_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#78;&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"25\" style=\"vertical-align: 0px;\"\/> in polynomial time. Since no one has yet succeeded in doing so, the majority of scientists assume that <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-ee2f9a81a22c9b462a866558bf2513f5_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#80;&#32;&#92;&#110;&#101;&#113;&#32;&#78;&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"17\" width=\"61\" style=\"vertical-align: -4px;\"\/>. In concrete terms, a proof of the <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-b96195cbb695083f95874f351090f15c_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#80;&#45;&#78;&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"59\" style=\"vertical-align: 0px;\"\/> problem would mean that a computer can &#8220;efficiently&#8221; calculate, for example, the shortest tour in a TSP in a short time. However, a proof could also have negative consequences, e.g. in encryption technology. If <img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/erlebnisland-mathematik.de\/wp-content\/ql-cache\/quicklatex.com-184aa60f913c33eb50601f76b7a7caca_l3.png\" class=\"ql-img-inline-formula quicklatex-auto-format\" alt=\"&#80;&#32;&#61;&#32;&#78;&#80;\" title=\"Rendered by QuickLaTeX.com\" height=\"13\" width=\"61\" style=\"vertical-align: 0px;\"\/> were to apply, there would be the possibility that encryption systems could be cracked in a very short time. As a result, banks&#8217; security systems, among others, could be easily breached and our banking data would no longer be secure.<\/div>\n<p>[\/vc_column_text][vc_column_text]<\/p>\n<\/div>\n<div>\n<h3>Literature<\/h3>\n<p>[\/vc_column_text][vc_column_text][1] Nitzsche, Manfred: Graphen f\u00fcr Einsteiger. Springer, 2005<\/p>\n<p>[2] https:\/\/www.spektrum.de\/news\/loesung-fuer-p-np-problem\/1494941<\/p>\n<p>[3] https:\/\/en.wikipedia.org\/wiki\/Travelling_salesman_problem<\/p>\n<p>[4] https:\/\/en.wikipedia.org\/wiki\/P_versus_NP_problem\u00a0[\/vc_column_text][\/vc_column][\/vc_row][vc_row][vc_column][vc_column_text]<\/p>\n<\/div>\n<\/div>\n<p>[\/vc_column_text][\/vc_column][\/vc_row]<\/p>\n<\/div>","protected":false},"excerpt":{"rendered":"<p>[vc_row drowwidth=&#8221;sidebar-biest-default sidebar-biest&#8221;][vc_column][vc_column_text] Round trips through Saxony Imagine you are planning a round trip through the largest cities in Saxony. You only want to visit each city once and the round trip should be as short as possible. The &#8220;Round trip through Saxony&#8221; exhibit allows you to plan your journey as efficiently as possible. [\/vc_column_text][vc_single_image <a href=\"https:\/\/erlebnisland-mathematik.de\/en\/advanced-text-round-trips-through-saxony\/\" class=\"more-link\">&#8230;<span class=\"screen-reader-text\">  Round trips through Saxony<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_acf_changed":false,"footnotes":""},"folder":[],"class_list":["post-4970","page","type-page","status-publish","hentry"],"acf":[],"_links":{"self":[{"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/pages\/4970","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/comments?post=4970"}],"version-history":[{"count":21,"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/pages\/4970\/revisions"}],"predecessor-version":[{"id":4994,"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/pages\/4970\/revisions\/4994"}],"wp:attachment":[{"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/media?parent=4970"}],"wp:term":[{"taxonomy":"folder","embeddable":true,"href":"https:\/\/erlebnisland-mathematik.de\/en\/wp-json\/wp\/v2\/folder?post=4970"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}