[gmx-users] g_rotacf create tpr from pdb

[henri mone]

Dear Gromacs experts and newbies,

The program "g_rotacf" (calculates the autocorrelation function)
requires as input for the -s option either a "tpr", "tpb" or "tpa"
file.
I does not accept for the -s option a PDB file :- ( .
How can I create from a "pdb" file a "tpr" file?
The program "pdb2gmx" can only create from a  "pdb a "top" or  "gro"
file but no "tpr" file.
I also tried "grompp" but this needs a "mdp" file.

Making it short here are my two questions:
1. How do I create for "g_rotacf" a  "tpr", "tpb" or "tpa" file?
2. "g_rotacf" only extracts the coordinates from the xtc trajectory
why does it need a topology file (via  "tpr", "tpb" or "tpa").


Thanks any help is welcome
Henri