/**
* Calculate equivalent nodes
*
* Calculate groups of nodes, which are contained in their respective
* transitive reflexive closure in the automaton.
*
* Returns an automaton consisting of nodes, which each links to such a
* node group.
*
* @param slCountingSingleOccurenceAutomaton $automaton
* @return void
*/
protected function calculateEquivalencyAutomaton(slAutomaton $automaton)
{
$nodeValues = $automaton->getNodes();
$nodes = array_keys($nodeValues);
$nodeCount = count($nodes);
$equivalent = array();
$skip = array();
// Find equivalence classes in automaton
for ($i = 0; $i < $nodeCount; ++$i) {
if (isset($skip[$i])) {
continue;
}
$this->equivalenceClasses[$nodes[$i]] = array($nodes[$i]);
$equivalent[$nodes[$i]] = $nodes[$i];
for ($j = $i + 1; $j < $nodeCount; ++$j) {
if (in_array($nodes[$i], $automaton->transitiveClosure($nodes[$j])) && in_array($nodes[$j], $automaton->transitiveClosure($nodes[$i]))) {
$this->equivalenceClasses[$nodes[$i]][] = $nodes[$j];
$equivalent[$nodes[$j]] = $nodes[$i];
// The mutal containment in eachs reflexive transitive
// closure is obviously symetric
$skip[$j] = true;
}
}
}
// Readd edges between equivalency classes based on source automaton
$equivalencyAutomaton = new slAutomaton();
foreach ($this->equivalenceClasses as $name => $nodes) {
$equivalencyAutomaton->addNode($name);
foreach ($nodes as $node) {
foreach ($automaton->getOutgoing($node) as $dst) {
if ($name !== $equivalent[$dst]) {
$equivalencyAutomaton->addEdge($name, $equivalent[$dst]);
}
}
}
}
return $equivalencyAutomaton;
}
