GROMACS version: 2020
GROMACS modification: No
Dear all,
Concerning the gmx clustsize, below I have two questions on which you comments are highly appreciated;
(For a single frame)
gmx clustsize \
f conf.gro s conf.tpr nc nclust.xvg \
o csize.xpm ow csizew.xpm \
hc histoclust.xvg ac avclus.xvg \
temp temp.xvg cut 0.35 mol

I wonder if the “hc histoclust.xvg (or \frac{\text{histoclust.xvg}}{\text{Total number of clusters}})” gives a weighted histogram?

How does Gromacs calculate the average cluster size (ac avclus.xvg) for a frame?
The average value of a histogram is calculated as following
\frac{\sum\limits_{i=1}^{\textrm{max~size}}~(\text{(cluster size)}_i \times \text{(number of cluster with size}_i) )}{\sum\limits_{i=1}^{\textrm{max~size}}~\text{(number of cluster with size}_i)}
From “hc histoclust.xvg” for a sample frame, the above formula gives an average value much lower than what the “ac avclus.xvg” has reported for the frame!
Thank you
Salman