[gmx-users] g_select problem

[Albert]

Hello:

I would like to calculate the number of water molecules within 4A of 
residues number 400, and I try to run it with command:

g_select_mpi -f input.gro -sinput.gro -os water.xvg -sf selection.dat

here is my selection.dat:


waterO = resname SOL and name OW;
p = resnr 400 and Protein;
close = waterO and within 0.4 of p;
close;

However, it failed with messages:


Error in user input:
Invalid command-line options
   In command-line option -sf
     Error in parsing selections from file 'selection.dat'
       'p' is ambiguous

I am just wondering where is the problem?

Thanks a lot

Albert