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16 years ago
I tried to use this function, but got a not-defined error. Anyway, I have created a set of functions to replace this: 

<?php

//Since Correlation needs two arrays, I am hardcoding them
$array1[0] = 59.3;
$array1[1] = 61.2;
$array1[2] = 56.8
$array1[3] = 97.55;

$array2[0] = 565.82;
$array2[1] = 54.568;
$array2[2] = 84.22;
$array2[3] = 483.55;

//To find the correlation of the two arrays, simply call the  
//function Correlation that takes two arrays:

$correlation = Correlation($array1, $array2);

//Displaying the calculated Correlation:
print $correlation;

//The functions that work behind the scene to calculate the
//correlation

function Correlation($arr1, $arr2)
{        
    $correlation = 0;
    
    $k = SumProductMeanDeviation($arr1, $arr2);
    $ssmd1 = SumSquareMeanDeviation($arr1);
    $ssmd2 = SumSquareMeanDeviation($arr2);
    
    $product = $ssmd1 * $ssmd2;
    
    $res = sqrt($product);
    
    $correlation = $k / $res;
    
    return $correlation;
}

function SumProductMeanDeviation($arr1, $arr2)
{
    $sum = 0;
    
    $num = count($arr1);
    
    for($i=0; $i<$num; $i++)
    {
        $sum = $sum + ProductMeanDeviation($arr1, $arr2, $i);
    }
    
    return $sum;
}

function ProductMeanDeviation($arr1, $arr2, $item)
{
    return (MeanDeviation($arr1, $item) * MeanDeviation($arr2, $item));
}

function SumSquareMeanDeviation($arr)
{
    $sum = 0;
    
    $num = count($arr);
    
    for($i=0; $i<$num; $i++)
    {
        $sum = $sum + SquareMeanDeviation($arr, $i);
    }
    
    return $sum;
}

function SquareMeanDeviation($arr, $item)
{
    return MeanDeviation($arr, $item) * MeanDeviation($arr, $item);
}

function SumMeanDeviation($arr)
{
    $sum = 0;
    
    $num = count($arr);
    
    for($i=0; $i<$num; $i++)
    {
        $sum = $sum + MeanDeviation($arr, $i);
    }
    
    return $sum;
}

function MeanDeviation($arr, $item)
{
    $average = Average($arr);
    
    return $arr[$item] - $average;
}    

function Average($arr)
{
    $sum = Sum($arr);
    $num = count($arr);
    
    return $sum/$num;
}

function Sum($arr)
{
    return array_sum($arr);
}

?>
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