PROCEDURE: prestens PURPOSE: This function computes the relative components of the pressure tensor INPUT: dat: A 3d structure such as those gotten by using get_el,get_pl,etc. e.g. "get_el" KEYWORDS: esteprange: energy range to use CREATED BY: Davin Larson LAST MODIFICATION: @(#)prestens.pro 1.5 95/10/06 NOTE: It is NOT yet corrected to give physical results