  Recently, Gimbutas et al derived an elegant representation for the Green's
functions of Stokes flow in a half-space. We present a fast summation method
for sums involving these half-space Green's functions (stokeslets, stresslets
and rotlets) that consolidates and builds on the work by Klinteberg et al for
the corresponding free-space Green's functions. The fast method is based on two
main ingredients: The Ewald decomposition and subsequent use of FFTs. The Ewald
decomposition recasts the sum into a sum of two exponentially decaying series:
one in real-space (short-range interactions) and one in Fourier-space
(long-range interactions) with the convergence of each series controlled by a
common parameter. The evaluation of short-range interactions is accelerated by
restricting computations to neighbours within a specified distance, while the
use of FFTs accelerates the computations in Fourier-space thus accelerating the
overall sum. We demonstrate that while the method incurs extra costs for the
half-space in comparison to the free-space evaluation, greater computational
savings is also achieved when compared to their respective direct sums.
