The program is used for heavy atom structures with unknown heavy atom positions (including not-so-heavy-atoms like S or P).
When the user calls for PATTY, the system will automatically arrange for the following calculations: first calculate the Patterson function (program FOUR), then find the heavy atom(s) (program PATTY), and expand the partial structure (programs PHASEX, followed by FOUR), and finally recycle several times (programs PHASEX and FOUR) for further elucidation of the structure.