What does "RMSD distribution" actually mean for "gmx cluster -dist rmsd-dist.xvg"?

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GROMACS version:2021
GROMACS modification: No
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The manual says: -dist writes the RMSD distribution. But what does it actually mean?
The y-axis is “counts”, what is that? I only have 5418 frames, why the “counts” in total is 14674653?

This is the first a few lines of the rmsd-dist.xvg

@    title "RMS Distribution"
@    xaxis  label "RMS (nm)"
@    yaxis  label "counts"
@TYPE xy
         0           0
 0.0309454           0
 0.0618908           0
 0.0928362         411
  0.123782       12092
  0.154727       46490
  0.185672       87908
  0.216618      108481
  0.247563      103013
  0.278508       91346
  0.309454       75874
2

Hi,
the RMSD is calculated between all pair of structure. 14674653=N*(N-1) /2 where N is the number of frames and division by 2 is due to the fact that RMSD between A and B = RMSD between B and A.
\Alessandra

3

Hi Alessandra, thank you so much! That makes sense :)