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<a id="X81714DBC80CC4BCB" name="X81714DBC80CC4BCB"></a>
<div class="ChapSects"><a href="chap9_mj.html#X81714DBC80CC4BCB">9 Visualising and IO</a>
<div class="ContSect"> <a href="chap9_mj.html#X7CF67F8278D9469C">9.1 Visualising a digraph</a>

<div class="ContSSBlock">
 <a href="chap9_mj.html#X83B3318784E78415">9.1-1 Splash</a>
 <a href="chap9_mj.html#X7F9B99C478EE093A">9.1-2 DotDigraph</a>
 <a href="chap9_mj.html#X78DA31D1869D2F94">9.1-3 DotSymmetricDigraph</a>
 <a href="chap9_mj.html#X84120D447E2CAC23">9.1-4 DotPartialOrderDigraph</a>
 <a href="chap9_mj.html#X7F5653C8854FAEA6">9.1-5 DotPreorderDigraph</a>
 <a href="chap9_mj.html#X808D12CF81E2C19F">9.1-6 DotHighlightedDigraph</a>
</div></div>
<div class="ContSect"> <a href="chap9_mj.html#X81C9B1DC791C0BBD">9.2 Reading and writing digraphs to a file</a>

<div class="ContSSBlock">
 <a href="chap9_mj.html#X81FB5BE27903EC32">9.2-1 String</a>
 <a href="chap9_mj.html#X873D6EB8836A3C61">9.2-2 DigraphFromGraph6String</a>
 <a href="chap9_mj.html#X782A052979EA2376">9.2-3 Graph6String</a>
 <a href="chap9_mj.html#X87DD8B1E867760A5">9.2-4 DigraphFromDreadnautString</a>
 <a href="chap9_mj.html#X7923733D86767CE1">9.2-5 DIMACSString</a>
 <a href="chap9_mj.html#X7845ACDA7D4D333D">9.2-6 DigraphFile</a>
 <a href="chap9_mj.html#X7E8142007ED0CB9F">9.2-7 ReadDigraphs</a>
 <a href="chap9_mj.html#X82A4F0767C9EFC87">9.2-8 WriteDigraphs</a>
 <a href="chap9_mj.html#X86D531B287733561">9.2-9 IteratorFromDigraphFile</a>
 <a href="chap9_mj.html#X7AAA35867B5D8BF4">9.2-10 DigraphPlainTextLineEncoder</a>
 <a href="chap9_mj.html#X7808D99079295C22">9.2-11 TournamentLineDecoder</a>
 <a href="chap9_mj.html#X7DF22D1687D096D6">9.2-12 AdjacencyMatrixUpperTriangleLineDecoder</a>
 <a href="chap9_mj.html#X875393338486D77D">9.2-13 TCodeDecoder</a>
 <a href="chap9_mj.html#X8540FC21796A793F">9.2-14 PlainTextString</a>
 <a href="chap9_mj.html#X81BD23697857B244">9.2-15 WritePlainTextDigraph</a>
 <a href="chap9_mj.html#X804FDF6A7ED64049">9.2-16 WriteDIMACSDigraph</a>
 <a href="chap9_mj.html#X7BC595AF841B78A9">9.2-17 WholeFileEncoders</a>
</div></div>
</div>

<h3>9 Visualising and IO</h3>

<a id="X7CF67F8278D9469C" name="X7CF67F8278D9469C"></a>

<h4>9.1 Visualising a digraph</h4>

<a id="X83B3318784E78415" name="X83B3318784E78415"></a>

<h5>9.1-1 Splash</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Splash</code>( <var class="Arg">str</var>[, <var class="Arg">opts</var>] )</td><td class="tdright">( function )</td></tr></table></div>
Returns: Nothing.

This function attempts to convert the string <var class="Arg">str</var> into a pdf document and open this document, i.e. to splash it all over your monitor.

The string <var class="Arg">str</var> must correspond to a valid <code class="code">dot</code> or <code class="code">LaTeX</code> text file and you must have have <code class="code">GraphViz</code> and <code class="code">pdflatex</code> installed on your computer. For details about these file formats, see <a href="https://www.latex-project.org">https://www.latex-project.org</a> and <a href="https://www.graphviz.org">https://www.graphviz.org</a>.

This function is provided to allow convenient, immediate viewing of the pictures produced by the function <code class="func">DotDigraph</code> (<a href="chap9_mj.html#X7F9B99C478EE093A">9.1-2</a>).

The optional second argument <var class="Arg">opts</var> should be a record with components corresponding to various options, given below.

<dl>
<dt>path</dt>
<dd>this should be a string representing the path to the directory where you want <code class="code">Splash</code> to do its work. The default value of this option is <code class="code">"~/"</code>.

</dd>
<dt>directory</dt>
<dd>this should be a string representing the name of the directory in <code class="code">path</code> where you want <code class="code">Splash</code> to do its work. This function will create this directory if does not already exist.

The default value of this option is <code class="code">"tmp.viz"</code> if the option <code class="code">path</code> is present, and the result of <code class="func">DirectoryTemporary</code> (<a href="/home/runner/gap/doc/ref/chap9_mj.html#X8222B1A886E6195E">Reference: DirectoryTemporary</a>) is used otherwise.

</dd>
<dt>filename</dt>
<dd>this should be a string representing the name of the file where <var class="Arg">str</var> will be written. The default value of this option is <code class="code">"vizpicture"</code>.

</dd>
<dt>viewer</dt>
<dd>this should be a string representing the name of the program which should open the files produced by <code class="code">GraphViz</code> or <code class="code">pdflatex</code>.

</dd>
<dt>type</dt>
<dd>this option can be used to specify that the string <var class="Arg">str</var> contains a LaTeX or <code class="code">dot</code> document. You can specify this option in <var class="Arg">str</var> directly by making the first line <code class="code">"%latex"</code> or <code class="code">"//dot"</code>. There is no default value for this option, this option must be specified in <var class="Arg">str</var> or in <var class="Arg">opt.type</var>.

</dd>
<dt>engine</dt>
<dd>this option can be used to specify the GraphViz engine to use to render a <code class="code">dot</code> document. The valid choices are <code class="code">"dot"</code>, <code class="code">"neato"</code>, <code class="code">"circo"</code>, <code class="code">"twopi"</code>, <code class="code">"fdp"</code>, <code class="code">"sfdp"</code>, and <code class="code">"patchwork"</code>. Please refer to the GraphViz documentation for details on these engines. The default value for this option is <code class="code">"dot"</code>, and it must be specified in <var class="Arg">opt.engine</var>.

</dd>
<dt>filetype</dt>
<dd>this should be a string representing the type of file which <code class="code">Splash</code> should produce. For LaTeX files, this option is ignored and the default value <code class="code">"pdf"</code> is used.

</dd>
</dl>
This function was written by Attila Egri-Nagy and Manuel Delgado with some minor changes by J. D. Mitchell.

<div class="example"><pre>
gap> Splash(DotDigraph(RandomDigraph(4)));
</pre></div>

<a id="X7F9B99C478EE093A" name="X7F9B99C478EE093A"></a>

<h5>9.1-2 DotDigraph</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotDigraph</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( attribute )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotColoredDigraph</code>( <var class="Arg">digraph</var>, <var class="Arg">vert</var>, <var class="Arg">edge</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotVertexLabelledDigraph</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotVertexColoredDigraph</code>( <var class="Arg">digraph</var>, <var class="Arg">vert</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotEdgeColoredDigraph</code>( <var class="Arg">digraph</var>, <var class="Arg">edge</var> )</td><td class="tdright">( operation )</td></tr></table></div>
Returns: A string.

<code class="code">DotDigraph</code> produces a graphical representation of the digraph <var class="Arg">digraph</var>. Vertices are displayed as circles, numbered consistently with <var class="Arg">digraph</var>. Edges are displayed as arrowed lines between vertices, with the arrowhead of each line pointing towards the range of the edge.

<code class="code">DotColoredDigraph</code> differs from <code class="code">DotDigraph</code> only in that the values in given in the two lists are used to color the vertices and edges of the graph when displayed. The list for vertex colours should be a list of length equal to the number of vertices, containing strings that are accepted by the graphviz software, which is the one used for graph representation. The list for edge colours should be a list of lists with the same shape of the outneighbours of the digraph that contains strings that correspond to colours accepted by the graphviz software. If the lists are not the appropriate size, or have holes then the function will return an error.

<code class="code">DotVertexColoredDigraph</code> differs from <code class="code">DotDigraph</code> only in that the values in given in the list are used to color the vertices of the graph when displayed. The list for vertex colours should be a list of length equal to the number of vertices, containing strings that are accepted by the graphviz software, which is the one used for graph representation. If the list is not the appropriate size, or has holes then the function will return an error.

<code class="code">DotEdgeColoredDigraph</code> differs from <code class="code">DotDigraph</code> only in that the values in given in the list are used to color the vertices and edges of the graph when displayed. The list for edge colours should be a list of lists with the same shape of the outneighbours of the digraph that contains strings that correspond to colours accepted by the graphviz software. If the list is not the appropriate size, or has holes then the function will return an error.

<code class="code">DotVertexLabelledDigraph</code> differs from <code class="code">DotDigraph</code> only in that the values in <code class="func">DigraphVertexLabels</code> (<a href="chap5_mj.html#X7E51F2FE87140B32">5.1-12</a>) are used to label the vertices in the produced picture rather than the numbers <code class="code">1</code> to the number of vertices of the digraph.

The output is in <code class="code">dot</code> format (also known as <code class="code">GraphViz</code>) format. For details about this file format, and information about how to display or edit this format see <a href="https://www.graphviz.org">https://www.graphviz.org</a>.

The string returned by <code class="code">DotDigraph</code> or <code class="code">DotVertexLabelledDigraph</code> can be written to a file using the command <code class="func">FileString</code> (<a href="/home/runner/gap/pkg/gapdoc/doc/chap6_mj.html#X7E14D32181FBC3C3">GAPDoc: FileString</a>).

<div class="example"><pre>
gap> adj := List([1 .. 4], x -> [1, 1, 1, 1]);
[ [ 1, 1, 1, 1 ], [ 1, 1, 1, 1 ], [ 1, 1, 1, 1 ], [ 1, 1, 1, 1 ] ]
gap> adj[1][3] := 0;
0
gap> gr := DigraphByAdjacencyMatrix(adj);
<immutable digraph with 4 vertices, 15 edges>
gap> D := CompleteDigraph(4);
<immutable complete digraph with 4 vertices>
gap> vertcolors := [];;
gap> vertcolors[1] := "blue";; vertcolors[2] := "red";; 
gap> vertcolors[3] := "green";; vertcolors[4] := "yellow";;
gap> edgecolors := [];;
gap> edgecolors[1] := [];; edgecolors[2] := [];;
gap> edgecolors[3] := [];; edgecolors[4] := [];; 
gap> edgecolors[1][2] := "lightblue";;
gap> edgecolors[1][3] := "pink";;
gap> edgecolors[1][4] := "purple";;
gap> edgecolors[2][1] := "lightblue";;
gap> edgecolors[2][3] := "pink";; 
gap> edgecolors[2][4] := "purple";; 
gap> edgecolors[3][1] := "lightblue";; 
gap> edgecolors[3][2] := "pink";; 
gap> edgecolors[3][4] := "purple";;
gap> edgecolors[4][1] := "lightblue";; 
gap> edgecolors[4][2] := "pink";;
gap> edgecolors[4][3] := "purple";;
gap> Print(DotColoredDigraph(D, vertcolors, edgecolors));
//dot
digraph hgn{
node [shape=circle]
1[color=blue, style=filled]
2[color=red, style=filled]
3[color=green, style=filled]
4[color=yellow, style=filled]
1 -> 2[color=lightblue]
1 -> 3[color=pink]
1 -> 4[color=purple]
2 -> 1[color=lightblue]
2 -> 3[color=pink]
2 -> 4[color=purple]
3 -> 1[color=lightblue]
3 -> 2[color=pink]
3 -> 4[color=purple]
4 -> 1[color=lightblue]
4 -> 2[color=pink]
4 -> 3[color=purple]
}
gap> D := EmptyDigraph(3);
<immutable empty digraph with 3 vertices>
gap> vertcolors := [];;
gap> vertcolors[1] := "blue";; vertcolors[2] := "red";;
gap> vertcolors[3] := "green";;
gap> edgecolors := [];;
gap> edgecolors[1] := [];; edgecolors[2] := [];; 
gap> edgecolors[3] := [];;
gap> Print(DotColoredDigraph(D, vertcolors, edgecolors));
//dot
digraph hgn{
node [shape=circle]
1[color=blue, style=filled]
2[color=red, style=filled]
3[color=green, style=filled]
}
gap> D := Digraph([[2], [1, 3], [2]]);
<immutable digraph with 3 vertices, 4 edges>
gap> vertcolors := [];;
gap> vertcolors[1] := "blue";;
gap> vertcolors[2] := "pink";;
gap> vertcolors[3] := "purple";;
gap> edgecolors := [];;
gap> edgecolors[1] := [];; edgecolors[2] := [];;
gap> edgecolors[3] := [];;
gap> edgecolors[1][2] := "green";; edgecolors[2][1] := "green";;
gap> edgecolors[2][3] := "red";; edgecolors[3][2] := "red";;
gap> Print(DotSymmetricColoredDigraph(D, vertcolors, edgecolors));
//dot
graph hgn{
node [shape=circle]

1[color=blue, style=filled]
2[color=pink, style=filled]
3[color=purple, style=filled]
1 -- 2[color=green]
2 -- 3[color=red]
}
gap> D := Digraph([[2, 3], [1, 3], [1]]);
<immutable digraph with 3 vertices, 5 edges>
gap> vertcolors := [];;
gap> vertcolors[1] := "blue";; vertcolors[2] := "red";;
gap> vertcolors[3] := "green";;
gap> edgecolors := [];;
gap> edgecolors[1] := [];; edgecolors[2] := [];;
gap> edgecolors[3] := [];;
gap> edgecolors[1][2] := "orange";; edgecolors[1][3] := "yellow";;
gap> edgecolors[2][1] := "orange";; edgecolors[2][3] := "pink";;
gap> edgecolors[3][1] := "yellow";;
gap> Print(DotColoredDigraph(D, vertcolors, edgecolors));;
//dot
digraph hgn{
node [shape=circle]
1[color=blue, style=filled]
2[color=red, style=filled]
3[color=green, style=filled]
1 -> 2[color=orange]
1 -> 3[color=yellow]
2 -> 1[color=orange]
2 -> 3[color=pink]
3 -> 1[color=yellow]
}
gap> D := Digraph(IsMutableDigraph, [[2, 3], [1, 3], [1]]);
<mutable digraph with 3 vertices, 5 edges>
gap> vertcolors := [];;
gap> vertcolors[1] := "blue";; vertcolors[2] := "red";;
gap> vertcolors[3] := "green";;
gap> edgecolors := [];;
gap> edgecolors[1] := [];; edgecolors[2] := [];;
gap> edgecolors[3] := [];;
gap> edgecolors[1][2] := "orange";; edgecolors[1][3] := "yellow";;
gap> edgecolors[2][1] := "orange";; edgecolors[2][3] := "pink";;
gap> edgecolors[3][1] := "yellow";;
gap> Print(DotColoredDigraph(D, vertcolors, edgecolors));;
//dot
digraph hgn{
node [shape=circle]
1[color=blue, style=filled]
2[color=red, style=filled]
3[color=green, style=filled]
1 -> 2[color=orange]
1 -> 3[color=yellow]
2 -> 1[color=orange]
2 -> 3[color=pink]
3 -> 1[color=yellow]
}
gap> D;
<mutable digraph with 3 vertices, 5 edges>
gap> DotSymmetricDigraph(gr2){[12 .. 70]};
" hgn{\nnode [shape=circle]\n\n1\n2\n3\n4\n1 -- 2\n2 -- 3\n3 -- 3\n3 -"
gap> DotSymmetricDigraph(gr1);
Error, the argument <D> must be a symmetric digraph,
gap> D := CompleteDigraph(4);
<immutable complete digraph with 4 vertices>
gap> vertcolors := [];;
gap> vertcolors[1] := "blue";; vertcolors[2] := "red";; 
gap> vertcolors[3] := "green";; vertcolors[4] := "yellow";;
gap> Print(DotVertexColoredDigraph(D, vertcolors));
//dot
digraph hgn{
node [shape=circle]
1[color=blue, style=filled]
2[color=red, style=filled]
3[color=green, style=filled]
4[color=yellow, style=filled]
1 -> 2
1 -> 3
1 -> 4
2 -> 1
2 -> 3
2 -> 4
3 -> 1
3 -> 2
3 -> 4
4 -> 1
4 -> 2
4 -> 3
}
gap> D := CompleteDigraph(4);
<immutable complete digraph with 4 vertices>
gap> edgecolors := [];;
gap> edgecolors[1] := [];; edgecolors[2] := [];;
gap> edgecolors[3] := [];; edgecolors[4] := [];; 
gap> edgecolors[1][2] := "lightblue";;
gap> edgecolors[1][3] := "pink";;
gap> edgecolors[1][4] := "purple";;
gap> edgecolors[2][1] := "lightblue";;
gap> edgecolors[2][3] := "pink";; 
gap> edgecolors[2][4] := "purple";; 
gap> edgecolors[3][1] := "lightblue";; 
gap> edgecolors[3][2] := "pink";; 
gap> edgecolors[3][4] := "purple";;
gap> edgecolors[4][1] := "lightblue";; 
gap> edgecolors[4][2] := "pink";;
gap> edgecolors[4][3] := "purple";;
gap> Print(DotEdgeColoredDigraph(D, edgecolors));
//dot
digraph hgn{
node [shape=circle]
1
2
3
4
1 -> 2[color=lightblue]
1 -> 3[color=pink]
1 -> 4[color=purple]
2 -> 1[color=lightblue]
2 -> 3[color=pink]
2 -> 4[color=purple]
3 -> 1[color=lightblue]
3 -> 2[color=pink]
3 -> 4[color=purple]
4 -> 1[color=lightblue]
4 -> 2[color=pink]
4 -> 3[color=purple]
}
gap> FileString("dot/k4.dot", DotDigraph(gr));
154</pre></div>

<a id="X78DA31D1869D2F94" name="X78DA31D1869D2F94"></a>

<h5>9.1-3 DotSymmetricDigraph</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotSymmetricDigraph</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( attribute )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotSymmetricColoredDigraph</code>( <var class="Arg">digraph</var>, <var class="Arg">vert</var>, <var class="Arg">edge</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotSymmetricVertexColoredDigraph</code>( <var class="Arg">digraph</var>, <var class="Arg">vert</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotSymmetricEdgeColoredDigraph</code>( <var class="Arg">digraph</var>, <var class="Arg">edge</var> )</td><td class="tdright">( operation )</td></tr></table></div>
Returns: A string.

This function produces a graphical representation of the symmetric digraph <var class="Arg">digraph</var>. <code class="code">DotSymmetricDigraph</code> will return an error if <var class="Arg">digraph</var> is not a symmetric digraph. See <code class="func">IsSymmetricDigraph</code> (<a href="chap6_mj.html#X81B3EA7887219860">6.2-14</a>).

The function <code class="code">DotSymmetricColoredDigraph</code> differs from <code class="code">DotDigraph</code> only in that the values given in the two lists are used to color the vertices and edges of the graph when displayed. The list for vertex colours should be a list of length equal to the number of vertices, containing strings that are accepted by the graphviz software, which is the one used for graph representation. The list for edge colours should be a list of lists with the same shape of the outneighbours of the digraph that contains strings that correspond to colours accepted by the graphviz software. If the list is not the appropriate size, or has holes then the function will return an error.

The function <code class="code">DotSymmetricVertexColoredDigraph</code> differs from <code class="code">DotDigraph</code> only in that the values in given in the list is used to color the vertices of the graph when displayed. The list for vertex colours should be a list of length equal to the number of vertices, containing strings that are accepted by the graphviz software, which is the one used for graph representation. If the list is not the appropriate size, or has holes then the function will return an error.

The function <code class="code">DotSymmetricEdgeColoredDigraph</code> differs from <code class="code">DotDigraph</code> only in that the values given in the list are used to color the edges of the graph when displayed. The list for edge colours should be a list of lists with the same shape of the outneighbours, containing strings that are accepted by the graphviz software, which is the one used for graph representation. If the list is not the appropriate size, or has holes then the function will return an error.

Vertices are displayed as circles, numbered consistently with <var class="Arg">digraph</var>. Since <var class="Arg">digraph</var> is symmetric, for every non-loop edge there is a complementary edge with opposite source and range. <code class="code">DotSymmetricDigraph</code> displays each pair of complementary edges as a single line between the relevant vertices, with no arrowhead.

The output is in <code class="code">dot</code> format (also known as <code class="code">GraphViz</code>) format. For details about this file format, and information about how to display or edit this format see <a href="https://www.graphviz.org">https://www.graphviz.org</a>.

The string returned by <code class="code">DotSymmetricDigraph</code> can be written to a file using the command <code class="func">FileString</code> (<a href="/home/runner/gap/pkg/gapdoc/doc/chap6_mj.html#X7E14D32181FBC3C3">GAPDoc: FileString</a>).

<div class="example"><pre>
gap> star := Digraph([[2, 2, 3, 4], [1, 1], [1], [1, 4]]);
<immutable multidigraph with 4 vertices, 9 edges>
gap> IsSymmetricDigraph(star);
true
gap> FileString("dot/star.dot", DotSymmetricDigraph(gr));
gap> D := Digraph([[2], [1, 3], [2]]);
<immutable digraph with 3 vertices, 4 edges>
gap> vertcolors := [];;
gap> vertcolors[1] := "blue";;
gap> vertcolors[2] := "pink";;
gap> vertcolors[3] := "purple";;
gap> edgecolors := [];;
gap> edgecolors[1] := [];; edgecolors[2] := [];;
gap> edgecolors[3] := [];;
gap> edgecolors[1][2] := "green";; edgecolors[2][1] := "green";;
gap> edgecolors[2][3] := "red";; edgecolors[3][2] := "red";;
gap> Print(DotSymmetricColoredDigraph(D, vertcolors, edgecolors));
//dot
graph hgn{
node [shape=circle]

1[color=blue, style=filled]
2[color=pink, style=filled]
3[color=purple, style=filled]
1 -- 2[color=green]
2 -- 3[color=red]
}
gap> D := Digraph([[2], [1, 3], [2]]);
<immutable digraph with 3 vertices, 4 edges>
gap> vertcolors := [];;
gap> vertcolors[1] := "blue";;
gap> vertcolors[2] := "pink";;
gap> vertcolors[3] := "purple";;
gap> Print(DotSymmetricVertexColoredDigraph(D, vertcolors));
//dot
graph hgn{
node [shape=circle]

1[color=blue, style=filled]
2[color=pink, style=filled]
3[color=purple, style=filled]
1 -- 2
2 -- 3
}
gap> D := Digraph([[2], [1, 3], [2]]);
<immutable digraph with 3 vertices, 4 edges>
gap> edgecolors := [];;
gap> edgecolors[1] := [];; edgecolors[2] := [];;
gap> edgecolors[3] := [];;
gap> edgecolors[1][2] := "green";; edgecolors[2][1] := "green";;
gap> edgecolors[2][3] := "red";; edgecolors[3][2] := "red";;
gap> Print(DotSymmetricEdgeColoredDigraph(D, edgecolors));
//dot
graph hgn{
node [shape=circle]

1
2
3
1 -- 2[color=green]
2 -- 3[color=red]
}
83</pre></div>

<a id="X84120D447E2CAC23" name="X84120D447E2CAC23"></a>

<h5>9.1-4 DotPartialOrderDigraph</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotPartialOrderDigraph</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( attribute )</td></tr></table></div>
Returns: A string.

This function produces a graphical representation of a partial order digraph <var class="Arg">digraph</var>. <code class="code">DotPartialOrderDigraph</code> will return an error if <var class="Arg">digraph</var> is not a partial order digraph. See <code class="func">IsPartialOrderDigraph</code> (<a href="chap6_mj.html#X82BAE6D37D49A145">6.4-2</a>).

Since <var class="Arg">digraph</var> is a partial order, it is both reflexive and transitive. The output of <code class="code">DotPartialOrderDigraph</code> is the <code class="func">DotDigraph</code> (<a href="chap9_mj.html#X7F9B99C478EE093A">9.1-2</a>) of the <code class="func">DigraphReflexiveTransitiveReduction</code> (<a href="chap3_mj.html#X82AD17517E273600">3.3-14</a>) of <var class="Arg">digraph</var>.

The output is in <code class="code">dot</code> format (also known as <code class="code">GraphViz</code>) format. For details about this file format, and information about how to display or edit this format see <a href="https://www.graphviz.org">https://www.graphviz.org</a>.

The string returned by <code class="code">DotPartialOrderDigraph</code> can be written to a file using the command <code class="func">FileString</code> (<a href="/home/runner/gap/pkg/gapdoc/doc/chap6_mj.html#X7E14D32181FBC3C3">GAPDoc: FileString</a>).

<div class="example"><pre>
gap> poset := Digraph([[1, 4], [2], [2, 3, 4], [4]);
gap> IsPartialOrderDigraph(gr);
true
gap> FileString("dot/poset.dot", DotPartialOrderDigraph(gr));
83</pre></div>

<a id="X7F5653C8854FAEA6" name="X7F5653C8854FAEA6"></a>

<h5>9.1-5 DotPreorderDigraph</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotPreorderDigraph</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( attribute )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotQuasiorderDigraph</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( attribute )</td></tr></table></div>
Returns: A string.

This function produces a graphical representation of a preorder digraph <var class="Arg">digraph</var>. <code class="code">DotPreorderDigraph</code> will return an error if <var class="Arg">digraph</var> is not a preorder digraph. See <code class="func">IsPreorderDigraph</code> (<a href="chap6_mj.html#X8617726C7829F796">6.4-1</a>).

A preorder digraph is reflexive and transitive but in general it is not anti-symmetric and may have strongly connected components containing more than one vertex. The <code class="func">QuotientDigraph</code> (<a href="chap3_mj.html#X7D1D26D27F5B56C2">3.3-9</a>) <var class="Arg">Q</var> obtained by forming the quotient of <var class="Arg">digraph</var> by the partition of its vertices into the strongly connected components satisfies <code class="func">IsPartialOrderDigraph</code> (<a href="chap6_mj.html#X82BAE6D37D49A145">6.4-2</a>). Thus every vertex of <var class="Arg">Q</var> corresponds to a strongly connected component of <var class="Arg">digraph</var>. The output of <code class="code">DotPreorderDigraph</code> displays the <code class="func">DigraphReflexiveTransitiveReduction</code> (<a href="chap3_mj.html#X82AD17517E273600">3.3-14</a>) of <var class="Arg">Q</var> with vertices displayed as rounded rectangles labelled by all of the vertices of <var class="Arg">digraph</var> in the corresponding strongly connected component.

The output is in <code class="code">dot</code> format (also known as <code class="code">GraphViz</code>) format. For details about this file format, and information about how to display or edit this format see <a href="https://www.graphviz.org">https://www.graphviz.org</a>.

The string returned by <code class="code">DotPreorderDigraph</code> can be written to a file using the command <code class="func">FileString</code> (<a href="/home/runner/gap/pkg/gapdoc/doc/chap6_mj.html#X7E14D32181FBC3C3">GAPDoc: FileString</a>).

<div class="example"><pre>
gap> preset := Digraph([[1, 2, 4, 5], [1, 2, 4, 5], [3, 4], [4], [1, 2, 4, 5]);
gap> IsPreorderDigraph(gr);
true
gap> FileString("dot/preset.dot", DotProrderDigraph(gr));
83</pre></div>

<a id="X808D12CF81E2C19F" name="X808D12CF81E2C19F"></a>

<h5>9.1-6 DotHighlightedDigraph</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DotHighlightedDigraph</code>( <var class="Arg">digraph</var>, <var class="Arg">verts</var>[, <var class="Arg">colour1</var>, <var class="Arg">colour2</var>] )</td><td class="tdright">( operation )</td></tr></table></div>
Returns: A string.

<code class="code">DotHighlightedDigraph</code> produces a graphical representation of the digraph <var class="Arg">digraph</var>, where the vertices in the list <var class="Arg">verts</var>, and edges between them, are drawn with colour <var class="Arg">colour1</var> and all other vertices and edges in <var class="Arg">digraph</var> are drawn with colour <var class="Arg">colour2</var>. If <var class="Arg">colour1</var> and <var class="Arg">colour2</var> are not given then <code class="code">DotHighlightedDigraph</code> uses black and grey respectively.

Note that <code class="code">DotHighlightedDigraph</code> does not validate the colours <var class="Arg">colour1</var> and <var class="Arg">colour2</var> - consult the GraphViz documentation to see what is available. See <code class="func">DotDigraph</code> (<a href="chap9_mj.html#X7F9B99C478EE093A">9.1-2</a>) for more details on the output.

<div class="example"><pre>
gap> digraph := Digraph([[2, 3], [2], [1, 3]]);
<digraph with 3 vertices, 5 edges>
gap> FileString("dot/my_digraph.dot",
> DotHighlightedDigraph(digraph, [1, 2], "red", "black"));
264</pre></div>

<a id="X81C9B1DC791C0BBD" name="X81C9B1DC791C0BBD"></a>

<h4>9.2 Reading and writing digraphs to a file</h4>

This section describes different ways to store and read graphs from a file in the Digraphs package.

<dl>
<dt> Graph6 </dt>
<dd> Graph6 is a graph data format for storing undirected graphs with no multiple edges nor loops of size up to $ 2^{36} - 1 $ in printable characters. The format consists of two parts. The first part uses one to eight bytes to store the number of vertices. And the second part is the upper half of the adjacency matrix converted into ASCII characters. For a more detail description see <a href=" http://cs.anu.edu.au/~bdm/data/formats.txt">Graph6</a>.

</dd>
<dt> Sparse6 </dt>
<dd> Sparse6 is a graph data format for storing undirected graphs with possibly multiple edges or loops. The maximal number of vertices allowed is $ 2^{36} - 1 $. The format consists of two parts. The first part uses one to eight bytes to store the number of vertices. And the second part only stores information about the edges. Therefore, the Sparse6 format return a more compact encoding then Graph6 for sparse graph, i.e. graphs where the number of edges is much less than the number of vertices squared. For a more detail description see <a href=" http://cs.anu.edu.au/~bdm/data/formats.txt">Sparse6</a>.

</dd>
<dt> Digraph6 </dt>
<dd>Digraph6 is a new format based on Graph6 , but designed for digraphs. The entire adjacency matrix is stored, and therefore there is support for directed edges and single-vertex loops. However, multiple edges are not supported.

</dd>
<dt> DiSparse6 </dt>
<dd>DiSparse6 is a new format based on Sparse6 , but designed for digraphs. In this format the list of edges is partitioned into increasing and decreasing edges, depending whether the edge has its source bigger than the range. Then both sets of edges are written separately in Sparse6 format with a separation symbol in between.

</dd>
<dt> dreadnaut </dt>
<dd>dreadnaut is a graph data format designed for directed and undirected graphs. The format supports loops but multiple edges are ignored. The format consists of an initial section that defines the graph's structural properties, such as the number of vertices, the starting value for vertices, and whether the graph is directed. This is followed by a list of edges. For more information and examples of the format see nauty and Traces User's Guide</a>.

</dd>
<dt> DIMACS </dt>
<dd>DIMACS is a graph data format that can be used for symmetric digraphs. For a more detailed description, see <code class="func">WriteDIMACSDigraph</code> (<a href="chap9_mj.html#X804FDF6A7ED64049">9.2-16</a>)

</dd>
</dl>
<a id="X81FB5BE27903EC32" name="X81FB5BE27903EC32"></a>

<h5>9.2-1 String</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ String</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( attribute )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ PrintString</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( operation )</td></tr></table></div>
Returns: A string.

Returns a string <code class="code">string</code> such that <code class="code">EvalString(string)</code> is equal to <var class="Arg">digraph</var>, and has the same mutability. See <code class="func">EvalString</code> (<a href="/home/runner/gap/doc/ref/chap27_mj.html#X7DE4CCD285440659">Reference: EvalString</a>).

The methods installed for <code class="code">String</code> make some attempts to ensure that <code class="code">string</code> has as short a length as possible, but there may exist shorter strings that also evaluate to <var class="Arg">digraph</var>.

It is possible that <code class="code">string</code> may contain escaped special characters. To obtain a representation of <var class="Arg">digraph</var> that can be entered as GAP input, please use <code class="func">Print</code> (<a href="/home/runner/gap/doc/ref/chap6_mj.html#X7AFA64D97A1F39A3">Reference: Print</a>). Note that <code class="code">Print</code> for a digraph delegates to <code class="code">PrintString</code>, which delegates to <code class="code">String</code>.

<div class="example"><pre>
gap> D := CycleDigraph(3);
<immutable cycle digraph with 3 vertices>
gap> Print(D);
CycleDigraph(3);
gap> G := PetersenGraph(IsMutableDigraph);
<mutable digraph with 10 vertices, 30 edges>
gap> String(G);
"DigraphFromGraph6String(IsMutableDigraph, \"IheA@GUAo\");"
gap> Print(last);
DigraphFromGraph6String(IsMutableDigraph, "IheA@GUAo");
gap> DigraphFromGraph6String(IsMutableDigraph, "IheA@GUAo");
<mutable digraph with 10 vertices, 30 edges>
</pre></div>

<a id="X873D6EB8836A3C61" name="X873D6EB8836A3C61"></a>

<h5>9.2-2 DigraphFromGraph6String</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DigraphFromGraph6String</code>( [<var class="Arg">filt</var>, ]<var class="Arg">str</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DigraphFromDigraph6String</code>( [<var class="Arg">filt</var>, ]<var class="Arg">str</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DigraphFromSparse6String</code>( [<var class="Arg">filt</var>, ]<var class="Arg">str</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DigraphFromDiSparse6String</code>( [<var class="Arg">filt</var>, ]<var class="Arg">str</var> )</td><td class="tdright">( operation )</td></tr></table></div>
Returns: A digraph.

If <var class="Arg">str</var> is a string encoding a graph in Graph6, Digraph6, Sparse6 or DiSparse6 format, then the corresponding function returns a digraph. In the case of either Graph6 or Sparse6, formats which do not support directed edges, this will be a digraph such that for every edge, the edge going in the opposite direction is also present.

Each of these functions takes an optional first argument <var class="Arg">filt</var>, which should be either <code class="func">IsMutableDigraph</code> (<a href="chap3_mj.html#X7D7EDF83820ED6F5">3.1-2</a>) or <code class="func">IsImmutableDigraph</code> (<a href="chap3_mj.html#X7CAFAA89804F80BD">3.1-3</a>), and which specifies whether the output digraph shall be mutable or immutable. If no first argument is provided, then an immutable digraph is returned by default.

<div class="example"><pre>
gap> DigraphFromGraph6String("?");
<immutable empty digraph with 0 vertices>
gap> DigraphFromGraph6String("C]");
<immutable symmetric digraph with 4 vertices, 8 edges>
gap> DigraphFromGraph6String("H?AAEM{");
<immutable symmetric digraph with 9 vertices, 22 edges>
gap> DigraphFromDigraph6String("&?");
<immutable empty digraph with 0 vertices>
gap> DigraphFromDigraph6String(IsMutableDigraph, "&DOOOW?");
<mutable digraph with 5 vertices, 5 edges>
gap> DigraphFromDigraph6String("&CQFG");
<immutable digraph with 4 vertices, 6 edges>
gap> DigraphFromDigraph6String("&IM[SrKLc~lhesbU[F_");
<immutable digraph with 10 vertices, 51 edges>
gap> DigraphFromDiSparse6String(".CaWBGA?b");
<immutable multidigraph with 4 vertices, 9 edges>
</pre></div>

<a id="X782A052979EA2376" name="X782A052979EA2376"></a>

<h5>9.2-3 Graph6String</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Graph6String</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Digraph6String</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ Sparse6String</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DiSparse6String</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( operation )</td></tr></table></div>
Returns: A string.

These four functions return a highly compressed string fully describing the digraph <var class="Arg">digraph</var>.

Graph6 and Digraph6 are formats best used on small, dense graphs, if applicable. For larger, sparse graphs use Sparse6 and Disparse6 (this latter also preserves multiple edges).

See <code class="func">WriteDigraphs</code> (<a href="chap9_mj.html#X82A4F0767C9EFC87">9.2-8</a>).

<div class="example"><pre>
gap> gr := Digraph([[2, 3], [1], [1]]);
<immutable digraph with 3 vertices, 4 edges>
gap> Sparse6String(gr);
":Bc"
gap> DiSparse6String(gr);
".Bc{f"
</pre></div>

<a id="X87DD8B1E867760A5" name="X87DD8B1E867760A5"></a>

<h5>9.2-4 DigraphFromDreadnautString</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DigraphFromDreadnautString</code>( <var class="Arg">s</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DreadnautString</code>( <var class="Arg">digraph</var>[, <var class="Arg">partition</var>] )</td><td class="tdright">( operation )</td></tr></table></div>
These operations read or write a single digraph to or from a string in the dreadnaut format, as appropriate.

<code class="code">DigraphFromDreadnautString</code> expects the argument <var class="Arg">s</var> to be a string, containing a single graph in dreadnaut format, and returns a digraph.

If the vertices are not already 1-indexed, their labels will be reindexed by subtracting a constant offset so that the smallest label becomes 1, with the relative ordering of vertex labels being preserved. If a partition is explicitly specified, each vertex will be assigned a label corresponding to its part in the partition. Should the graph be undirected, the symmetric closure of the graph will be returned. See <code class="func">DigraphVertexLabels</code> (<a href="chap5_mj.html#X7E51F2FE87140B32">5.1-12</a>) and <code class="func">DigraphSymmetricClosure</code> (<a href="chap3_mj.html#X874883DD7DD450C4">3.3-12</a>).

<code class="code">DreadnautString</code> expects a digraph <var class="Arg">digraph</var> and returns a string in dreadnaut format. An optional second argument <var class="Arg">partition</var> may be provided, which should be a list of length equal to the number of vertices in <var class="Arg">digraph</var>. Each entry in the list assigns the corresponding vertex to a group, allowing you to specify a vertex partition. For example, if the digraph has three vertices and <var class="Arg">partition</var> is <code class="code">["a", "b", "a"]</code>, this would mean that the first and third vertices belong to the same part, and the second vertex belongs to a separate part. This partition will appear in the resulting string as a line of the form <code class="code">f = [...]</code>.

Note that <code class="func">WriteDigraphs</code> (<a href="chap9_mj.html#X82A4F0767C9EFC87">9.2-8</a>) does not support specifying a partition when writing a digraph to a file in dreadnaut format. To include a partition when writing to a file, use <code class="code">DreadnautString</code> to generate the string, then write it to a file using standard I/O functions. If <var class="Arg">digraph</var> has multiple edges, then <code class="code">DreadnautString</code> returns a digraph constructed from <var class="Arg">digraph</var> by removing all multiple edges.

A detailed description of commands and options in dreadnaut format can be found at <a href="http://pallini.di.uniroma1.it/Guide.html">nauty and Traces User's Guide. Of those commands, the following are supported: n, g (and all available subcommands), _ (underscore), __ (double underscore), f, $=#, $$, d, -d, "...", !

<div class="example"><pre>
gap> gr := Digraph([[2], [1, 3, 4], [2, 4], [2, 3]]);
<immutable digraph with 4 vertices, 8 edges>
gap> s := DreadnautString(gr);;
gap> DigraphFromDreadnautString(s) = gr;
true
gap> DreadnautString(gr, ["a", "b", "b", "a"]);
"n=4 $=1 d g\n1 : 2;\n2 : 1 3 4;\n3 : 2 4;\n4 : 2 3.\nf = [1 4 | 2 3]"</pre></div>

<a id="X7923733D86767CE1" name="X7923733D86767CE1"></a>

<h5>9.2-5 DIMACSString</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DIMACSString</code>( <var class="Arg">digraph</var> )</td><td class="tdright">( operation )</td></tr></table></div>
<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DigraphFromDIMACSString</code>( <var class="Arg">s</var> )</td><td class="tdright">( operation )</td></tr></table></div>
Returns: A string.

<code class="code">DIMACSString</code> takes a single symmetric digraph <var class="Arg">digraph</var>, and returns a string representation of <var class="Arg">digraph</var> in the DIMACS format.

<code class="code">DigraphFromDIMACSString</code> takes such a string and returns the single symmetric digraph which it describes.

For more information on the DIMACS format, see <code class="func">WriteDIMACSDigraph</code> (<a href="chap9_mj.html#X804FDF6A7ED64049">9.2-16</a>).

These functions support file-based DIMACS encoding and decoding through <code class="func">WriteDigraphs</code> (<a href="chap9_mj.html#X82A4F0767C9EFC87">9.2-8</a>) and <code class="func">ReadDigraphs</code> (<a href="chap9_mj.html#X7E8142007ED0CB9F">9.2-7</a>), for consistency with other encoders and decoders. Alternatively, <code class="func">WriteDIMACSDigraph</code> (<a href="chap9_mj.html#X804FDF6A7ED64049">9.2-16</a>) and <code class="func">ReadDIMACSDigraph</code> (<a href="chap9_mj.html#X804FDF6A7ED64049">9.2-16</a>) may be used for direct DIMACS I/O.

<div class="example"><pre>
gap> gr := Digraph([[2], [1, 3, 4], [2, 4], [2, 3]]);
<immutable digraph with 4 vertices, 8 edges>
gap> DIMACSString(gr);
"p edge 4 4\ne 1 2\ne 2 3\ne 2 4\ne 3 4\nn 1 1\nn 2 2\nn 3 3\nn 4 4"
gap> DigraphFromDIMACSString(last);
<immutable digraph with 4 vertices, 8 edges></pre></div>

<a id="X7845ACDA7D4D333D" name="X7845ACDA7D4D333D"></a>

<h5>9.2-6 DigraphFile</h5>

<div class="func"><table class="func" width="100%"><tr><td class="tdleft"><code class="func">‣ DigraphFile</code>( <var class="Arg">filename</var>[, <var class="Arg">coder</var>][, <var class="Arg">mode</var>] )</td><td class="tdright">( function )</td></tr></table></div>
Returns: An IO file object.

If <var class="Arg">filename</var> is a string representing the name of a file, then <code class="code">DigraphFile</code> returns an <a href="https://gap-packages.github.io/io">IO</a> package file object for that file.

If the optional argument <var class="Arg">coder</var> is specified and is a function which either encodes a digraph as a string, or decodes a string into a digraph, then this function will be used when reading or writing to the returned file object. If the optional argument <var class="Arg">coder</var> is not specified, then the encoding of the digraphs in the returned file object must be specified in the the file extension. The file extension must be one of: <code class="code">.g6</code>, <code class="code">.s6</code>, <code class="code">.d6</code>, <code class="code">.ds6</code>, <code class="code">.txt</code>, <code class="code">.p</code>, or <code class="code">.pickle</code>; more details of these file formats is given below.

If the optional argument <var class="Arg">mode</var> is specified, then it must be one of: <code class="code">"w"</code> (for write), <code class="code">"a"</code> (for append), or <code class="code">"r"</code> (for read). If <var class="Arg">mode</var> is not specified, then <code class="code">"r"</code> is used by default.

If <var class="Arg">filename</var> ends in one of: <code class="code">.gz</code>, <code class="code">.bz2</code>, or <code class="code">.xz</code>, then the digraphs which are read from, or written to, the returned file object are decompressed, or compressed, appropriately.

The file object returned by <code class="code">DigraphFile</code> can be given as the first argument for either of the functions <code class="func">ReadDigraphs</code> (<a href="chap9_mj.html#X7E8142007ED0CB9F">9.2-7</a>) or <code class="func">WriteDigraphs</code> (<a href="chap9_mj.html#X82A4F0767C9EFC87">9.2-8</a>). The purpose of this is to reduce the overhead of recreating the file object inside the functions <code class="func">ReadDigraphs</code> (<a href="chap9_mj.html#X7E8142007ED0CB9F">9.2-7</a>) or <code class="func">WriteDigraphs</code> (<a href="chap9_mj.html#X82A4F0767C9EFC87">9.2-8</a>) when, for example, reading or writing many digraphs in a loop.

The currently supported file formats, and associated filename extensions, are:

<dl>
<dt>graph6 (.g6)</dt>
<dd>A standard and widely-used format for undirected graphs, with no support for loops or multiple edges. Only symmetric graphs are allowed -- each edge is combined with its converse edge to produce a single undirected edge. This format is best used for "dense" graphs -- those with many edges per vertex.

</dd>
<dt>sparse6 (.s6)</dt>
<dd>Unlike graph6, sparse6 has support for loops and multiple edges. However, its use is still limited to symmetric graphs. This format is better-suited to "sparse" graphs -- those with few edges per vertex.

</dd>
<dt>digraph6 (.d6)</dt>
<dd>This format is based on graph6, but stores direction information - therefore is not limited to symmetric graphs. Loops are allowed, but multiple edges are not. Best compression with "dense" graphs.

</dd>
<dt>disparse6 (.ds6)</dt>
<dd>Any type of digraph can be encoded in disparse6: directions, loops, and multiple edges are all allowed. Similar to sparse6, this has the best compression rate with "sparse" graphs.

</dd>
<dt>plain text (.txt)</dt>
<dd>This is a human-readable format which stores graphs in the form <code class="code">0 7 0 8 1 7 2 8 3 8 4 8 5 8 6 8</code> i.e. pairs of vertices describing edges in a graph. More specifically, the vertices making up one edge must be separated by a single space, and pairs of vertices must be separated by two spaces.

See <code class="func">ReadPlainTextDigraph</code> (<a href="chap9_mj.html#X81BD23697857B244">9.2-15</a>) for a more flexible way to store digraphs in a plain text file.

</dd>
<dt>pickled (<code class="file">.p</code> or <code class="file">.pickle</code>)</dt>
<dd>Digraphs are pickled using the <a href="https://gap-packages.github.io/io">IO</a> package. This is particularly good when the <code class="func">DigraphGroup</code> (<a href="chap7_mj.html#X803ACEDA7BBAC5B3">7.2-10</a>) is non-trivial.

</dd>
<dt>dreadnaut (.dre)</dt>
<dd>A graph format designed for directed and undirected graphs. The format supports loops but multiple edges are ignored. The format consists of an initial section that defines the graph's structural properties, such as the number of vertices, the starting value for vertices, and whether the graph is directed. This is followed by a list of edges. For more information and examples of the format see nauty and Traces User's Guide</a>.

</dd>
<dt> DIMACS (.dimacs) </dt>
<dd>A graph format that can be used for symmetric digraphs. For a more detailed description, see <code class="func">WriteDIMACSDigraph</code> (<a href="chap9_mj.html#X804FDF6A7ED64049">9.2-16</a>)

</dd>
</dl>

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