線形回帰の単回帰をPHPで実装 ref: http://qiita.com/sinri/items/fcca46db672ea3d9c1ea

file0.txt

/**
* Copyright 2015 Sinri Edogawa.
*/
class LinearRegression
{
    private $xs;
    private $ys;
    private $element_count;

    private $a;
    private $b;

    function __construct()
    {
        $this->xs=array();
        $this->ys=array();
        $this->element_count=0;
    }

    public function addElement($x,$y){
        $this->xs[]=$x;
        $this->ys[]=$y;
        $this->element_count+=1;
    }

    //y=a+bx
    public function getConstBase(){
        return $this->a;
    }
    public function getParamFactor(){
        return $this->b;
    }

    public function computeLR(){
        if($this->element_count<=0)return false;
        if($this->element_count!=count($this->xs) || $this->element_count!=count($this->ys))return false;
        $x_sum=0;
        $y_sum=0;
        for ($i=0; $i < $this->element_count; $i++) { 
            $x_sum+=$this->xs[$i];
            $y_sum+=$this->ys[$i];
        }
        $x_ave=1.0*$x_sum/$this->element_count;
        $y_ave=1.0*$y_sum/$this->element_count;

        $up=0;
        $down=0;

        for ($i=0; $i < $this->element_count; $i++) { 
            $up+=($this->xs[$i]-$x_ave)*($this->ys[$i]-$y_ave);
            $down+=($this->xs[$i]-$x_ave)*($this->xs[$i]-$x_ave);
        }   
        if($down==0)return false;
        $this->b=$up/$down;
        $this->a=$y_ave-$x_ave*$this->b;
        return true;
    }
}

file1.txt

$LR=new LinearRegression();

//xとyのペアを繰り返して記録する
$LR->addElement($x,$y);

$lr_done=$LR->computeLR();
if($lr_done){
    echo "y=".$LR->getConstBase()."+".$LR->getParamFactor()."x";
}else{
    echo "FAILED";
}