function stockVariance()
{
$i = 0;
foreach ($this->_stocks as $stock) {
$matrix = new Finance_Matrix($this->ArrayRet[$stock], $this->ArrayRet[$stock]);
$this->variances[$i] = round($matrix->Covariance($this->ArrayRet[$stock], $this->ArrayRet[$stock]), 4);
$i++;
}
return $this->variances;
}
