def error(self, start, end) -> float:
        """Return the approximation cost on the segment [start:end].

        Args:
            start (int): start of the segment
            end (int): end of the segment

        Returns:
            segment cost

        Raises:
            NotEnoughPoints: when the segment is too short (less than `min_size` samples).
        """
        if end - start < self.min_size:
            raise NotEnoughPoints
        sub = self.signal[start:end]
        med = np.median(sub, axis=0)

        return abs(sub - med).sum()
Return the approximation cost on the segment [start:end].

        Args:
            start (int): start of the segment
            end (int): end of the segment

        Returns:
            segment cost

        Raises:
            NotEnoughPoints: when the segment is too short (less than `min_size` samples).
        
src/ruptures/costs/costl1.py