On 08/29/2012 09:33 PM, Bala subramanian wrote:
Hi Mark,
Thanks. I tried defining the rdist in several ways and each time i get
an error as follows, and the last definition of rdist is infact very
similar to what is shown in examples.Could you suggest what is the
mistake i'm doing here.

You're still not following the example. You have to measure a distance from a point to a point, and (for example) your first attempt is leaving both definitions vague. The example uses "res_com distance from com..." for a reason.

g_select -select 'rdist = res_com distance from com of group Protein; resname SOL and rdist >= 0.25 and rdist <= .5'

Mark


selection parser: invalid expression value for parameter 'from'

Definitions of rdist. My protein contains 16 alanine residues in water box.

rdist = distance from atom of group "Protein"; resname SOL and rdist
=0.2 and rdist <=0.5
rdist = distance from atom of resnr 1 to 16; resname SOL and rdist
=0.25 and rdist <=0.5
rdist = res_com distance from atom of resnr 1 to 16; resname SOL and
rdist >=0.25 and rdist <=0.5
rdist = atom distance from atom of resname ALA; resname SOL and rdist
=0.25 and rdist <=0.5
rdist = res_com distance from atom of resname ALA; resname SOL and
rdist >=0.25 and rdist <=0.5

thanks

On Wed, Aug 29, 2012 at 11:59 AM, Mark Abraham <mark.abra...@anu.edu.au> wrote:
On 29/08/2012 7:43 PM, Bala subramanian wrote:
Hi,
I read the examples. I find that one example shows the usage of rdist
keyword. But i am not getting the right syntax to use it. I tried
several ways as follows to find water within .25-5 nm. Could someone
help me here.

-select 'resname SOL and within (0.25 and 0.5)  of group "Protein"'
-select 'resname SOL and rdist>=0.25 and rdist <=0.5  of group "Protein"'
-select 'resname SOL and within 0.25-0.5 of group "Protein"'
-select 'resname SOL and (rdist >=.25 and rdist <=0.5) of group "Protein"
'
-select 'resname SOL and within (rdist >= 0.25 and rdist <= 0.5) of
group "Protein"'
-select 'resname SOL and within {0.25 to 0.5}  of group "Protein"'

The examples that use rdist take care to define it on the previous line,
which you haven't.

Mark



On Tue, Aug 28, 2012 at 5:56 PM, Mark Abraham <mark.abra...@anu.edu.au>
wrote:
On 29/08/2012 1:37 AM, Bala subramanian wrote:
Friends,
I read the documentation of g_select and previous questions, but I
could nt find how to extract the index of water layer around the
protein. While i understand that i can use 'within' keyword to get
water layer around protein, my need is slightly different in a sense
that i have specify a range of distances. For instance: Water at 2.5
to 5.0 Ang from protein etc.

I tried something like within 0.25 to 0.5, within 0.25-0.5 etc, but i
was not successful.

g_select -select "help examples" has some useful starting material. You
want
atoms whose distance is greater than 0.25 and less than 0.5, so ask for
that.

Mark
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