Re: [AMBER] Problems with RMSF calculations

From: <>
Date: Mon, 29 Jun 2020 13:46:47 -0700

   Hi Daniel,

   Thanks a lot for the clarification. I agree with you that the RMSF of the
   pd1 and pd2 would not be the average of the individual RMSFs of pd1 and pd2.
   But I was thinking that it would be somewhere close to the average value and
   not greater than of the larger of the two RMSFs (for my case pd1).

   I tried to play with the example you gave with a simpler system and I do see
   that RMSF1234 > RMSF12 and RMSF1234 > RMSF34 when using the RMSF formula
   that contains the deviation from the average value (see Case I in the
   attached png).

   However, when I replace this formula and compute deviations wrt a reference
   value (see Case II), I do get RMSF34 > RMSF1234 > RMSF12. Since I do supply
   a reference frame (first frame) I would have expected cpptraj to be doing
   something like Case II.

   If indeed the formula being used is similar to the Case I formula then what
   is the use of the reference. Using the average position as reference (as
   Kenneth suggested earlier) seems redundant.

   Thanks a lot for all the help!


   From: [1]Daniel Roe
   Sent: 29 June 2020 09:02
   To: [2]AMBER Mailing List
   Subject: Re: [AMBER] Problems with RMSF calculations


   On Fri, Jun 26, 2020 at 2:49 PM <> wrote:

> I would expect the RMSF calculated using this script to give the

> RMSF from the two production runs

   This isn't correct, and the short explanation is because the RMSF

   calculation involves a square root. You can convince yourself of this

   by taking a simple set of numbers (like 4 5 3 4) and plug them into

   the RMSF formula ( RMSF1234 = sqrt(AvgSumSq - Avg^2), where AvgSumSq

   is the average of the sum of squares of the values and Avg is the

   average of the values. Then calculate RMSF for the first two and last

   two values (call them RMSF12 and RMSF34). You'll see that the average

   of RMSF12 and RMSF34 is not RMSF1234. Hope this helps,


> using the input above is not the true average of the two trajectories.



> The attached graph will make it clearer.

> comp_mean.png contains the RMSF calculated using cpptraj for the entire

> and PD2 and for PD1 + PD2. I have also plotted here the mean RMSFs (for

> chunks) for PD 1 and PD 2 that I calculated using python. Am I using

> RMSF script incorrectly? I want to calculate the residue-wise

> of the Ca atoms of the peptide backbone of my entire simulation (i.e.
   PD 1

> and 2 combined).



> Thanks a lot in advance for all the help!


> Kartik Lakshmi Rallapalli


> References


> 1.;!!Mih3wA!RkWVHZ9uzYaTsfRwSkKOl8

> 2.

> 3.;!!Mih3wA!RkWVHZ9uzYaTsfRwSkKOl8

> 4.

> 5.;!!Mih3wA!RkWVHZ9uzYaTsfRwSkKOl8

> 6.

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Received on Mon Jun 29 2020 - 14:00:03 PDT
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