[gmx-users] g_sgangle & dihedrals

[Matteo Masetti]

Hi all,
I'm trying to calculate the value of some dihedral angles of my protein
as a function of time with the tool g_sgangle.
I was very surprised when I've checked my results, and I found out that
g_sgangle only reports positive values, even when they should be
negative!

I mean, g_sgangle calculate a dihedral angle of (say) 10 degrees, while
the same angle is -10 degrees when evaluated with vmd (using the same
sequence of atom numbers). I think it mustn't be  a problem of how the
planes are defined... For the example above, I could understand a value
of 350, but 10 (when the correct value is -10) in my opinion is
absolutely meaningless...

As i've read in the archive, I set up my index file for the dihedral
1-2-3-4 as follows:

[plane 1]
1 2 3
[plane 2]
2 3 4

Has anybody experienced this behavoiour before??!?
Any help or clue will be very appreciated!
Thanks!