% Impulse response invariant discretization of fractional order
% irid_fod function is prepared to compute a discrete-time finite dimensional
% (z) transfer function to approximate a continuous irrational transfer
% function s^r, where "s" is the Laplace transform variable, and "r" is a
% real number in the range of (-1,1). s^r is called a fractional order
% differentiator if 0 < r < 1 and a fractional order integrator if -1 < r < 0.
% The proposed approximation keeps the impulse response "invariant"
% r: the fractional order
% Ts: the sampling period
% norder: the finite order of the approximate z-transfer function
% (the orders of denominator and numerator z-polynomial are the same)
% sr: returns the LTI object that approximates the s^r in the sense
% of impulse response.
% TEST CODE
% Reference: YangQuan Chen. "Impulse-invariant and step-invariant
% discretization of fractional order integrators and differentiators".
% August 2008. CSOIS AFC (Applied Fractional Calculus) Seminar.
YangQuan Chen (2021). Impulse response invariant discretization of fractional order integrators/differentiators (https://www.mathworks.com/matlabcentral/fileexchange/21342-impulse-response-invariant-discretization-of-fractional-order-integrators-differentiators), MATLAB Central File Exchange. Retrieved .
Inspired: OS4_FOC, Fractional Order Flight Control of Quadrotor UAS: A Simscape Benchmark Environment and A Case Study, Step response invariant discretization of fractional order integrators/differentiators, Impulse response invariant discretization of fractional order low-pass filters
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