[gmx-users] Re: Re: g_bundle problem

[Stefan Hoorman]

>
> Stefan Hoorman wrote:
> >
> >     Stefan Hoorman wrote:
> >      > I have tried using g_bundle in order to analyse helix axes in my
> >      > transmembran helices. I created two groups in my ndx file that
> >     included
> >      > the alpha carbons of the first half of my helix and a second
> >     group for
> >      > the alpha carbons for the second half. When I try using g_bundle
> the
> >      > following error comes up:
> >      > "Fatal error:
> >      > The size of one of your index groups is not a multiple of n"
> >      > What am I doing wrong?
> >
> >     Not a clue - What is your exact command line?  How many atoms are in
> >     each index
> >     group?  The value of n is the number of parts into which the axes
> >     are divided
> >     and there are several criteria in the code that must be met, else
> >     you get this
> >     error.  So without this information, the best guess is: some
> >     criterion is not
> >     being met.
> >
> >     -Justin
> >
> >      > Thank you
> >      >
> >
> >     --
> >
> >     g_bundle analyzes bundles of axes - and therefore number of atoms
> >     each group
> >     have to be divisible by number of axes (entered by -na). And I
> >     suppose, you
> >     are interested in analyzing only one axis, don't you?
> >
> >     Milan
> >
> >
> > Well, the exact command line was : g_bundle -f md.xtc -s md.tpr -z -n
> > bundle.ndx
> > As for analyzing one axis, yes, that is true, I am only interested in
> > analysing my helix principal axis.
> > I have tried using different group sizes for the index group. I have
> > tried using only carbon alpha for the first half and then for the second
> > half (each had 15 alpha carbons), then I tried with all sorts of
> > different groups, first five residues and last five residues, first
> > fifteen residues and so on.
> > All analysis came up with the same error.
> >
>
> You're not setting the -na flag, which by default is zero.  In the code, if
> the
> value from -na (int n) is <= 0, you get the fatal error.  Maybe the error
> message should be made more specific, so that users actually know what n
> is.
> You need to explicitly set a value for -na >= 1.
>
> -Justin
>
>
Right, thank you Justin, things worked out nicely now. I was able to
calculatemy helix tilt with respect to the z axis. Would there be a way to
calculate the tilt between two helix axes? I cannot simply calculate the
tilt of each with respect to the z axis and subtract because the
interhelical tilt does not depend only on the z axis. Can g_bundle give me
that kind of information?
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