Re: imprecision in table energy

From: Jim Phillips (jim_at_ks.uiuc.edu)
Date: Mon Sep 25 2006 - 14:10:00 CDT

NAMD uses an interpolation table for r^-12 (VDWA), r^-6 (VDWB), and
Coulomb interactions (FAST, SCOR, etc). It also reports the maximum
errors and the radii at which they occurs. This looks normal. Note that
large absolute errors at small radii are basically floating-point
precision, while large relative errors near the cutoff distance are tiny
in absolute terms.

-Jim

On Sun, 24 Sep 2006, A. Ozlem T. Bishop wrote:

>
> Hi there,
> Could you please explain what this is. Should I be concerned about it or ignore it?
>
> thanks
> ozlem
>
> Info: ABSOLUTE IMPRECISION IN FAST TABLE ENERGY: 3.70577e-22 AT 11.9974
> Info: RELATIVE IMPRECISION IN FAST TABLE ENERGY: 6.62384e-17 AT 11.9974
> Info: ABSOLUTE IMPRECISION IN FAST TABLE FORCE: 9.09495e-13 AT 0.03125
> Info: RELATIVE IMPRECISION IN FAST TABLE FORCE: 4.21309e-16 AT 11.9138
> Info: ABSOLUTE IMPRECISION IN SCOR TABLE ENERGY: 2.91168e-22 AT 11.9974
> Info: RELATIVE IMPRECISION IN SCOR TABLE ENERGY: 6.16001e-17 AT 11.9974
> Info: ABSOLUTE IMPRECISION IN SCOR TABLE FORCE: 1.98523e-22 AT 11.9974
> Info: RELATIVE IMPRECISION IN SCOR TABLE FORCE: 8.0593e-16 AT 11.9138
> Info: ABSOLUTE IMPRECISION IN VDWA TABLE ENERGY: 2.75 AT 0.0441942
> Info: RELATIVE IMPRECISION IN VDWA TABLE ENERGY: 6.72641e-14 AT 11.9138
> Info: ABSOLUTE IMPRECISION IN VDWA TABLE FORCE: 6656 AT 0.0441942
> Info: RELATIVE IMPRECISION IN VDWA TABLE FORCE: 2.055e-15 AT 0.0441942
> Info: ABSOLUTE IMPRECISION IN VDWB TABLE ENERGY: 7.45058e-09 AT 0.0441942
> Info: RELATIVE IMPRECISION IN VDWB TABLE ENERGY: 7.56853e-15 AT 11.9138
> Info: ABSOLUTE IMPRECISION IN VDWB TABLE FORCE: 7.62939e-06 AT 0.0441942
> Info: RELATIVE IMPRECISION IN VDWB TABLE FORCE: 7.96546e-16 AT 11.9138
>
>
>
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