9. Conclusion

Clearly, we have only scratched the surface of the problem of designing an observer to estimate certain variables of a dynamic system described by differential equations in an unnoisy setting. Apart from the fact that for non-linear models, this question is still largely open, many methods of designing observers such as sliding-mode observers, differential observers, finite-time observers where the estimation error is zero after a certain time, or other types of estimators have not been addressed. Nor have we discussed the algebraic techniques for estimating the derivatives of signals