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    stats_covariance

    (PECL stats >= 1.0.0)

    stats_covariance — Computes the covariance of two data sets

    説明

    stats_covariance(array $a, array $b): float

    Returns the covariance of a and b.

    パラメータ

    a

    The first array

    b

    The second array

    戻り値

    Returns the covariance of a and b, or false on failure.

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    User Contributed Notes 2 notes

    up
    3
    Angel J. Salinas
    9 years ago
    // kanniprabu's function is wrong.
    // You can check this function with COVARIANCE.P Excel function:

    function getCovariance( $valuesA, $valuesB )
    {
    $countA = count($valuesA);
    $countB = count($valuesB);
    if ( $countA != $countB ) {
    trigger_error( 'Arrays with different sizes: countA='. $countA .', countB='. $countB, E_USER_WARNING );
    return false;
    }

    if ( $countA < 0 ) {
    trigger_error( 'Empty arrays', E_USER_WARNING );
    return false;
    }

    // Use library function if available
    if ( function_exists( 'stats_covariance' ) ) {
    return stats_covariance( $valuesA, $valuesB );
    }

    $meanA = array_sum( $valuesA ) / floatval( $countA );
    $meanB = array_sum( $valuesB ) / floatval( $countB );
    $add = 0.0;

    for ( $pos = 0; $pos < $countA; $pos++ ) {
    $valueA = $valuesA[ $pos ];
    if ( ! is_numeric( $valueA ) ) {
    trigger_error( 'Not numerical value in array A at position '. $pos .', value='. $valueA, E_USER_WARNING );
    return false;
    }

    $valueB = $valuesB[ $pos ];
    if ( ! is_numeric( $valueB ) ) {
    trigger_error( 'Not numerical value in array B at position '. $pos .', value='. $valueB, E_USER_WARNING );
    return false;
    }

    $difA = $valueA - $meanA;
    $difB = $valueB - $meanB;
    $add += ( $difA * $difB );
    } // for

    return $add / floatval( $countA );
    }
    up
    -2
    kanniprabu at gmail dot com
    11 years ago
    <?php
    //Covariance Calculation
    function standard_covariance($aValues,$bValues)
    {
    $a= (array_sum($aValues)*array_sum($bValues))/count($aValues);
    $ret = array();
    for(    $i=0;$i<count($aValues);$i++)
    {
    $ret[$i]=$aValues[$i]*$bValues[$i];
    }
    $b=(array_sum($ret)-$a)/(count($aValues)-1);
    return (float)     $b;
    }
    $aValues=array(3,4,5,7);
    $bValues=array(10,11,13,14);
    echo     standard_covariance($aValues,$bValues);
    ?>
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