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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Received on Fri Jul 22 2016 - 06:00:07 PDT
