This paper firstly deals with finite time stability (FTS) of Riemann-Liouville fractional delay differential equations via giving a series of properties of delayed matrix function of Mittag-Leffler. We secondly study relative controllability of such type-controlled system. With the help of the representation of solution, both Gram-like type matrix and rank criterion are derived, which extend the corresponding results for linear systems.
KEYWORDSdelayed matrix function of Mittag-Leffler, finite time stability, fractional delay differential equations, relative controllability
INTRODUCTIONRecently, some authors apply delayed exponential matrix function to find the explicit solution formula of linear delay equations. 1-3 Further, there are some continued work on finding the representation of solutions to delay continuous and discrete systems; see, for example, previous studies. [4][5][6][7][8][9][10][11] Fractional differential equations have been used in solving the practical problems in the fields of natural science. 12,13 In particular, FTS of linear fractional delay differential equations with controls was offered in Lazarević, 14 and an inequality of Gronwall type is used to derive the results. For other related contribution, one can refer to previous works. [15][16][17][18][19][20][21][22][23][24][25] However, an initial singular condition for the Riemann-Liouville fractional differential equations is much different from the standard initial condition for a Caputo fractional differential equations. The main results of the standard initial condition for a Caputo fractional delay differential equation were obtained in Li and Wang. 11 Relative controllability and its related problems of linear systems represented by different type delay systems have been studied in literature. [26][27][28][29][30][31][32][33] In particular, rank and Kalman criteria for relative controllability are studied extensively.Very recently, Li and Wang 12 studiedHere, D − + x denotes Riemann-Liouville fractional derivative, I 1− − + x denotes Riemann-Liouville fractional integral, T = k * < ∞ for a fixed k * ∈ {1, 2, … }, is a constant, ∈ C([− , T], R n ), and (D − + )( ) exists. We consider the Riemann-Liouville fractional derivative D − + , where the lower limit is − + (− is a singular point). To keep the "consistence" with the lower limit in Riemann-Liouville derivative, we keep the initial condition at − + .