From: Axel Kohlmeyer (
Date: Tue Oct 13 2009 - 11:29:09 CDT


you have to be careful with precence between operators.
if you want to make sure that an expression is evaluated
in a specific order, use parenthesis.

On Tue, Oct 13, 2009 at 11:39 AM, Joseph Bylund <> wrote:
> Based on my understanding of selection syntax these two expressions should
> select an identical subset of atoms, however that's not what I'm
> experiencing. Should there be a difference and if so how can one interpret
> these two expressions
> "carbon and within 5 of resid 500"
> and
> "within 5 of resid 500 and carbon"

the first would select all carbon and then take a "within 5 of resid 500"
selection in that.

the second case would take a within 5 of (resid 500 and carbon)
this way the within should select atoms of any kind, which is obviously
not the same.

is this what you are seeing?


> Thanks,
> -Joe

Dr. Axel Kohlmeyer
Institute for Computational Molecular Science
College of Science and Technology
Temple University, Philadelphia PA, USA.