src/Maths/Algebra/Matrix.php
public function validX()
    {
        return (bool) (!is_null($this->keyX()) && isset($this->data[$this->keyX(true)]));
    }
public function validX()
    {
        return (bool) (!is_null($this->keyX()) && isset($this->data[$this->keyX(true)]));
    }
Test if current `x` line is valid

@return  bool