Editing Poisson summation formula (section)

===Ewald summation===
Computationally, the Poisson summation formula is useful since a slowly converging summation in real space is guaranteed to be converted into a quickly converging equivalent summation in Fourier space.<ref>[[Philip Woodward|Woodward, Philipp M.]] (1953). ''Probability and Information Theory, with Applications to Radar''. Academic Press, p. 36.</ref> (A broad function in real space becomes a narrow function in Fourier space and vice versa.)  This is the essential idea behind [[Ewald summation]].