B.M.  Mohan, Sanjeeb Kumar  Kar, 
    Estimation and Optimal Control with Reduced Order Observers via Orthogonal Functions,
    International Journal of System Signal Control and Engineering Application,
    Volume 3,Issue 1,
    2010,
    Pages 1-6,
    ISSN 1997-5422,
    ijssceapp.2010.1.6,
    (https://makhillpublications.co/view-article.php?doi=ijssceapp.2010.1.6)
    Abstract: Using Block-Pulse Functions (BPFs) and Shifted Legendre Polynomials (SLPs) 2 recursive algorithms are presented for the analysis of linear time-invariant optimal control systems using reduced order observers. An illustrative example is included to demonstrate the superiority of proposed recursive algorithms over the existing recursive/nonrecursive approaches.
    Keywords: shifted legendre polynomials;Optimal control;observer;orthogonal functions;block-pulse functions