We propose and analyze an efficient discretization of the Mittag-Leffler operator function
where A is a self-adjoint positive-definite operator. This function has a broad field of applications. Thus, it specifies a solution operator for the evolutionary problem ∂tu + ∂t−𝛼 Au = 0, t > 0, u(0) = u0, that includes a spatial operator A and its fractional time derivative of order 𝛼 (in the Riemann–Liouville sense), i.e., u(t) = E1+𝛼(−At1+𝛼)u0. We apply the method of Cayley transform, which allows us to recursively separate the variables and represent the Mittag-Leffler function in the form of an infinite series of products of the Laguerre–Cayley functions with respect to the time variable (i.e., polynomials in t1+𝛼) and the powers of Cayley transform for the spatial operator. The approximate representation has the form of a truncated series with N terms. We estimate the accuracy of the N-term approximation scheme depending on 𝛼 and N.
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Published in Ukrains’kyi Matematychnyi Zhurnal, Vol. 74, No. 5, pp. 620–634, May, 2022. Ukrainian DOI: https://doi.org/10.37863/umzh.v74i5.7097.
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Gavrilyuk, I.P., Makarov, V.L. Approximations of the Mittag-Leffler Operator Function with Exponential Accuracy and Their Applications to Solving Evolutionary Equations with Fractional Time Derivative. Ukr Math J 74, 709–725 (2022). https://doi.org/10.1007/s11253-022-02096-0
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DOI: https://doi.org/10.1007/s11253-022-02096-0