PROCEDURE: add_all PURPOSE: adds user defined structure elements to the 3d structures. USAGE: add_all,dat,add INPUT: dat: A (3d) data structure. add: a structure such as: {vsw:'Vp' , magf:'B3', sc_pos:'pos'} RESULTS: for the above example, the elements, vsw, magf, and sc_pos are added to the dat structure. The values are obtained from the tplot variables 'Vp', 'B3' and 'pos' respectively.