Two atoms for distance calculation have to be in same selection thus program expects even number of positions and do not get in my opinion.You could show your index.ndx for better investigation.
On Monday, August 21, 2017, 9:24:35 PM GMT+3, Sotirios Dionysios I. Papadatos <si.papada...@edu.cut.ac.cy> wrote: Hi, I am trying to calculate the distance between two atoms, which are defined in an index file. The command that I use is: "gmx distance -f output.gro -s prod.tpr -n index.ndx -oav distance.xvg" I get the obvious: "Selection 'atom_name' does not evaluate into an even number of positions (there are 1 positions)" The same happens if I use in -f prod.trr What might be wrong? Any insights on what to look for? What usually gives this kind of error? Feel free to ask for any further information. Thanks in advance -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists * For (un)subscribe requests visit https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a mail to gmx-users-requ...@gromacs.org. -- Gromacs Users mailing list * Please search the archive at http://www.gromacs.org/Support/Mailing_Lists/GMX-Users_List before posting! * Can't post? Read http://www.gromacs.org/Support/Mailing_Lists * For (un)subscribe requests visit https://maillist.sys.kth.se/mailman/listinfo/gromacs.org_gmx-users or send a mail to gmx-users-requ...@gromacs.org.