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| <?php | |
| namespace CirrusSearch\Search\Rescore; | |
| use CirrusSearch\SearchConfig; | |
| use Elastica\Query\FunctionScore; | |
| /** | |
| * Saturation function based on x/(k+x), k is a parameter | |
| * to control how fast the function saturates. | |
| * NOTE: that satu is always 0.5 when x == k. | |
| * Parameter a is added to form a sigmoid : x^a/(k^a+x^a) | |
| * Based on http://research.microsoft.com/pubs/65239/craswell_sigir05.pdf | |
| * This function is suited to apply a new factor in a weighted sum. | |
| */ | |
| class SatuFunctionScoreBuilder extends FunctionScoreBuilder { | |
| /** @var float */ | |
| private $k; | |
| /** @var float */ | |
| private $a; | |
| /** @var string */ | |
| private $field; | |
| /** | |
| * @param SearchConfig $config | |
| * @param float $weight | |
| * @param array $profile | |
| * @throws InvalidRescoreProfileException | |
| */ | |
| public function __construct( SearchConfig $config, $weight, $profile ) { | |
| parent::__construct( $config, $weight ); | |
| if ( isset( $profile['k'] ) ) { | |
| $this->k = $this->getOverriddenFactor( $profile['k'] ); | |
| if ( $this->k <= 0 ) { | |
| throw new InvalidRescoreProfileException( 'Param k must be > 0' ); | |
| } | |
| } else { | |
| throw new InvalidRescoreProfileException( 'Param k is mandatory' ); | |
| } | |
| if ( isset( $profile['a'] ) ) { | |
| $this->a = $this->getOverriddenFactor( $profile['a'] ); | |
| if ( $this->a <= 0 ) { | |
| throw new InvalidRescoreProfileException( 'Param a must be > 0' ); | |
| } | |
| } else { | |
| $this->a = 1; | |
| } | |
| if ( isset( $profile['field'] ) ) { | |
| $this->field = $profile['field']; | |
| } else { | |
| throw new InvalidRescoreProfileException( 'Param field is mandatory' ); | |
| } | |
| } | |
| public function append( FunctionScore $functionScore ) { | |
| $formula = $this->getScript(); | |
| $functionScore->addScriptScoreFunction( new \Elastica\Script\Script( $formula, null, | |
| 'expression' ), null, $this->weight ); | |
| } | |
| /** | |
| * @return string | |
| */ | |
| public function getScript() { | |
| $formula = "pow(doc['{$this->field}'].value , {$this->a}) / "; | |
| $formula .= "( pow(doc['{$this->field}'].value, {$this->a}) + "; | |
| $formula .= "pow({$this->k},{$this->a}))"; | |
| return $formula; | |
| } | |
| } |