public function offsetGet($index)
    {
        if (!isset($this->a[$index])) {
            throw new InvalidArgumentException('Element not found at the'
                . " given offset $index.");
        }

        return $this->a[$index];
    }
public function offsetGet($index)
    {
        if (!isset($this->a[$index])) {
            throw new InvalidArgumentException('Element not found at the'
                . " given offset $index.");
        }

        return $this->a[$index];
    }
public function offsetGet ( $ index ) { if ( ! isset ( $ this -> a [ $ index ] ) ) { throw new InvalidArgumentException ( 'Element not found at the' . " given offset $index." ) ; } return $ this -> a [ $ index ] ; }
Return a row from the matrix at the given index.

@param mixed $index
@throws \InvalidArgumentException
@return int|float
Return a row from the matrix at the given index .