International
Tables for Crystallography Volume B Reciprocal space Edited by U. Shmueli © International Union of Crystallography 2006 
International Tables for Crystallography (2006). Vol. B, ch. 1.3, p. 81

Conjugate symmetric (Section 1.3.2.4.2.3) implies that if the data X are real and symmetric [i.e. and ], then so are the results . Thus if contains a centre of symmetry, F is real symmetric. There is no distinction (other than notation) between structurefactor and electrondensity calculation; the algorithms will be described in terms of the former. It will be shown that if , a real symmetric transform can be computed with only partial transforms instead of .