The internal implementation of VFE/DTC are non-standard and need references to their derivations.
Related literature:
VFE: M. K. Titsias. "Variational learning of inducing variables in sparse Gaussian
processes". In: Proceedings of the Twelfth International Conference on Artificial
Intelligence and Statistics. 2009.
DTC: M. Seeger, C. K. I. Williams and N. D. Lawrence. "Fast Forward Selection to Speed Up
Sparse Gaussian Process Regression". In: Proceedings of the Ninth International Workshop on
Artificial Intelligence and Statistics. 2003
The internal implementation of VFE/DTC are non-standard and need references to their derivations.
Related literature:
https://github.com/JuliaGaussianProcesses/AbstractGPs.jl/pull/308#issuecomment-1084420431
CC: @willtebbutt