Create random graphs with php and graphiz

randgraph.php

<?php

$maxN = 10;
$maxE = 20;

// generate random edges
$e = [];
for($n = 1; $n <= $maxE; $n++) {
	$e[] = [rand(1, $maxN), rand(1, $maxN)];
}

// remove duplicates and self-loops
$dup = [];
foreach($e as $i => $v) {
	if ($v[0] == $v[1]) {
		unset($e[$i]);
	}
	$d = $v[0].':'.$v[1];
	if (isset($dup[$d])) {
		unset($e[$i]);
	} else {
		$dup[$d] = true;
	}
}

$graph = <<<EOF
digraph example {
	rankdir=LR;
	graph [ dpi = 300 ];
	size="8,5"
	node [shape = circle];

EOF;

foreach($e as $edge) {
	list($from, $to) = $edge;
	$graph .= "$from -> $to;\n";
}

$graph .= "}\n";

echo $graph;

Usage:

php randgraph.php > graph.dot
dot -O -Tpng graph.dot