There does seem to be a problem. I'll look into it further and get
back to you. Thanks for the report.
-Dan
On Fri, Jul 22, 2016 at 6:22 AM, Markus Schneider
<markus.schneider2.mytum.de> wrote:
> Hi,
>
> during analysis of "multidihedral" generated torsion datasets with the
> "stat" command, I encountered an unexpected result. Compared to my own
> calculations, the "c" and "g+" bin occupancies are different. I expected
> that the "c" bin would contain angles from -30 to +30 deg and "g+" would
> contain the range from +30 to +90 deg.
>
> The raw multidihedral output data is in the range [-180,+180]. When I
> bin the raw data myself, I can reproduce the result of cpptraj's stat
> analysis exactly if I set the c bin to [-30,0] and the g+ bin to [0,90].
> When I set the bins to the expected values above, I get more data points
> in the c bin, while fewer are placed in the g+ bin. I would like to ask
> whether there might be an error with how the stat command bins the data.
>
> The relevant code piece in Analysis_Statistics.cpp seems to be:
>
> double value = ds.Dval( i );
> double dval = value;
> if (dval < 0) dval += 360;
> *curbin = (int) (dval - 30.0) / 60;*
>
> I suspect that the last line might be responsible for the observation.
> The first three lines, as I infer, provide that dval is transformed to
> the range [0,360]. I created a test in C for the last line:
>
> --------------
>
> int bin(double angle)
> {
> return (int) (angle - 30.0) / 60;
> }
>
> int main()
> {
> double angles[] = {0.0,29.0,30.0,89.0,90.0,149.0,
> 150.0,209.0,210.0,269.0,270.0,329.0,330.0,359.0};
> for(int i=0;i<14;i++){
> printf("angle: %.1f bin: %d\n",angles[i],bin(angles[i]));
> }
>
> return 0;
> }
>
> --------------
>
> which creates the following output:
>
> angle: 0.0 bin: 0
> angle: 29.0 bin: 0
> angle: 30.0 bin: 0
> angle: 89.0 bin: 0
> angle: 90.0 bin: 1
> angle: 149.0 bin: 1
> angle: 150.0 bin: 2
> angle: 209.0 bin: 2
> angle: 210.0 bin: 3
> angle: 269.0 bin: 3
> angle: 270.0 bin: 4
> angle: 329.0 bin: 4
> angle: 330.0 bin: 5
> angle: 359.0 bin: 5
>
> According to bin definitions above, I expect that the angles 0 and 29
> deg should be part of bin 5. Instead, it seems that stat's g+ bin (0)
> ranges from 0 to 90, while the c bin (5) ranges from 330 to 0. This is
> consistent with my manual calculations. What do you think about this?
>
> This was tested with a fresh build of AmberTools 16.
>
> Best,
>
> Markus
>
>
>
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--
-------------------------
Daniel R. Roe, PhD
Department of Medicinal Chemistry
University of Utah
30 South 2000 East, Room 307
Salt Lake City, UT 84112-5820
http://home.chpc.utah.edu/~cheatham/
(801) 587-9652
(801) 585-6208 (Fax)
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Received on Thu Jul 28 2016 - 14:30:03 PDT
