Least Squares Method

LSM.php

<?php
/**
 * Created by PhpStorm.
 * User: kayladnls
 * Date: 12/19/14
 * Time: 4:20 PM
 */

$x = [1, 2, 3, 4, 5];
$y = [2, 4, 5, 4, 5];
$barx = [];
$bary = [];

$mean_x = calculateMean($x);
$mean_y = calculateMean($y);
$mean_intercept = [$mean_x, $mean_y];

//calculate x - barx
foreach ($x as $idx => $point)
{
    $barx[$idx] = $point - $mean_x;
}

//calculate y - bary
foreach ($y as $idx => $point)
{
    $bary[$idx] = $point - $mean_y;
}

$slope = findSlope($barx, $bary);

$yint = calcYInt($slope, $mean_intercept);

function calcYInt($slope, $mean_intercept)
{
    return $mean_intercept[1] - ($slope * $mean_intercept[0]);
}

function yhat($x, $yint, $slope)
{
    return $yint + ($slope * $x);
}

function findSlope($barx, $bary)
{
    $barxsq = squareArr($barx);

    $barx_times_bary = multArrs($barx, $bary);

    return calcSum($barx_times_bary) / calcSum($barxsq);
}

function multArrs($array1, $arry2)
{
    $multiplied = [];
    foreach ($array1 as $idx => $first)
    {
        $multiplied[] = $first * $arry2[$idx];
    }
    return $multiplied;
}

function squareArr(array $vals)
{
    $return = [];
    foreach ($vals as $val)
    {
        $return[] = $val*$val;
    }
    return $return;
}

function calculateMean(array $vals)
{
    return calcSum($vals) / count($vals);
}

function calcSum(array $vals)
{
    $sum = 0;
    foreach ($vals as $val)
    {
        $sum += $val;
    }
    return $sum;
}