Matlab function irid_fod. Impulse response invariant discretization of fractional order integrators/differentiators. 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.