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1 | <?php |
2 | |
3 | namespace CirrusSearch\Search\Rescore; |
4 | |
5 | use CirrusSearch\SearchConfig; |
6 | use Elastica\Query\FunctionScore; |
7 | |
8 | /** |
9 | * Saturation function based on x/(k+x), k is a parameter |
10 | * to control how fast the function saturates. |
11 | * NOTE: that satu is always 0.5 when x == k. |
12 | * Parameter a is added to form a sigmoid : x^a/(k^a+x^a) |
13 | * Based on http://research.microsoft.com/pubs/65239/craswell_sigir05.pdf |
14 | * This function is suited to apply a new factor in a weighted sum. |
15 | */ |
16 | class SatuFunctionScoreBuilder extends FunctionScoreBuilder { |
17 | /** @var float */ |
18 | private $k; |
19 | /** @var float */ |
20 | private $a; |
21 | /** @var string */ |
22 | private $field; |
23 | |
24 | /** |
25 | * @param SearchConfig $config |
26 | * @param float $weight |
27 | * @param array $profile |
28 | * @throws InvalidRescoreProfileException |
29 | */ |
30 | public function __construct( SearchConfig $config, $weight, $profile ) { |
31 | parent::__construct( $config, $weight ); |
32 | if ( isset( $profile['k'] ) ) { |
33 | $this->k = $this->getOverriddenFactor( $profile['k'] ); |
34 | if ( $this->k <= 0 ) { |
35 | throw new InvalidRescoreProfileException( 'Param k must be > 0' ); |
36 | } |
37 | } else { |
38 | throw new InvalidRescoreProfileException( 'Param k is mandatory' ); |
39 | } |
40 | |
41 | if ( isset( $profile['a'] ) ) { |
42 | $this->a = $this->getOverriddenFactor( $profile['a'] ); |
43 | if ( $this->a <= 0 ) { |
44 | throw new InvalidRescoreProfileException( 'Param a must be > 0' ); |
45 | } |
46 | } else { |
47 | $this->a = 1; |
48 | } |
49 | |
50 | if ( isset( $profile['field'] ) ) { |
51 | $this->field = $profile['field']; |
52 | } else { |
53 | throw new InvalidRescoreProfileException( 'Param field is mandatory' ); |
54 | } |
55 | } |
56 | |
57 | public function append( FunctionScore $functionScore ) { |
58 | $formula = $this->getScript(); |
59 | $functionScore->addScriptScoreFunction( new \Elastica\Script\Script( $formula, null, |
60 | 'expression' ), null, $this->weight ); |
61 | } |
62 | |
63 | /** |
64 | * @return string |
65 | */ |
66 | public function getScript() { |
67 | $formula = "pow(doc['{$this->field}'].value , {$this->a}) / "; |
68 | $formula .= "( pow(doc['{$this->field}'].value, {$this->a}) + "; |
69 | $formula .= "pow({$this->k},{$this->a}))"; |
70 | |
71 | return $formula; |
72 | } |
73 | } |