On the Solution Existence for Collocation Discretizations of Time-Fractional Subdiffusion Equations

Time-fractional parabolic equations with a Caputo time derivative of order α∈(0,1) are discretized in time using continuous collocation methods. For such discretizations, we give sufficient conditions for existence and uniqueness of their solutions. Two approaches are explored: the Lax–Milgram Theorem and the eigenfunction expansion. The resulting sufficient conditions, which involve certain m×m matrices (where m is the order of the collocation scheme), are verified both analytically, for all m≥1 and all sets of collocation points, and computationally, for all m≤20. The semilinear case is also addressed.