Clarify what setting zero to some output mdp options does

Change-Id: I36dc059e982c3358cbfa55596e71093ce3208446

diff --git a/docs/user-guide/mdp-options.rst b/docs/user-guide/mdp-options.rst
index b9901f7b70b1eb1c670721119422b0759ce157bd..0dbb525a32afbb1308fb95b18d975d75f0893784 100644 (file)
--- a/docs/user-guide/mdp-options.rst
+++ b/docs/user-guide/mdp-options.rst
@@ -358,24 +358,30 @@ Output control
    (0) [steps]
    number of steps that elapse between writing coordinates to the output
    trajectory file (:ref:`trr`), the last coordinates are always written
+   unless 0, which means coordinates are not written into the trajectory
+   file.
 
 .. mdp:: nstvout
 
    (0) [steps]
    number of steps that elapse between writing velocities to the output
    trajectory file (:ref:`trr`), the last velocities are always written
+   unless 0, which means velocities are not written into the trajectory
+   file.
 
 .. mdp:: nstfout
 
    (0) [steps]
    number of steps that elapse between writing forces to the output
-   trajectory file (:ref:`trr`), the last forces are always written.
+   trajectory file (:ref:`trr`), the last forces are always written,
+   unless 0, which means forces are not written into the trajectory
+   file.
 
 .. mdp:: nstlog
 
    (1000) [steps]
    number of steps that elapse between writing energies to the log
-   file, the last energies are always written
+   file, the last energies are always written.
 
 .. mdp:: nstcalcenergy
 
@@ -400,7 +406,8 @@ Output control
 
    (0) [steps]
    number of steps that elapse between writing position coordinates
-   using lossy compression (:ref:`xtc` file)
+   using lossy compression (:ref:`xtc` file), 0 for not writing
+   compressed coordinates output.
 
 .. mdp:: compressed-x-precision