public function covariance() : self
    {
        $b = $this->subtract($this->mean());

        return $b->matmul($b->transpose())
            ->divide($this->m);
    }
public function covariance() : self
    {
        $b = $this->subtract($this->mean());

        return $b->matmul($b->transpose())
            ->divide($this->m);
    }
public function covariance ( ) : self { $ b = $ this -> subtract ( $ this -> mean ( ) ) ; return $ b -> matmul ( $ b -> transpose ( ) ) -> divide ( $ this -> m ) ; }
Compute the covariance of this matrix and return it in a tuple along with
the computed mean.

@return self
Compute the covariance of this matrix and return it in a tuple along with the computed mean .