From e4d3494ab2b16cf9451186c3c35346a0ae38ee18 Mon Sep 17 00:00:00 2001 From: sjplimp Date: Mon, 6 Aug 2012 21:19:58 +0000 Subject: [PATCH] git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@8532 f3b2605a-c512-4ea7-a41b-209d697bcdaa --- doc/kspace_modify.html | 18 ++++++++++++++---- doc/kspace_modify.txt | 18 ++++++++++++++---- 2 files changed, 28 insertions(+), 8 deletions(-) diff --git a/doc/kspace_modify.html b/doc/kspace_modify.html index 96f4f64c7b..ac9ff227d8 100644 --- a/doc/kspace_modify.html +++ b/doc/kspace_modify.html @@ -120,10 +120,20 @@ This keyword gives you that option. PPPM method to compute forces on particles given electrostatic potentials on the PPPM mesh. The ik approach is the default. It performs differentiation in Kspace, but uses 3 FFTs to transfer the -computed fields back to real space. The analytic differentiation, or -ad approach uses only 1 FFT to transfer the computed fields back to -real space, but requires a somewhat larger PPPM mesh to achieve the -same accuracy as the ik approach. +computed fields back to real space (total of 4 FFTs per timestep). The +analytic differentiation, or ad approach uses only 1 FFT to transfer +the computed fields back to real space (total of 2 FFTs per timestep), +but requires a somewhat larger PPPM mesh to achieve the same accuracy +as the ik approach. +

+

IMPORTANT NOTE: Currently, only the pppm style supports the ad +option. Support from other pppm variants will be added later. +

+

IMPORTANT NOTE: If you run the ad option with a constant pressure +simulation (e.g. with fix npt), you may see a net +slow-down. This is because the ad option requires more expensive +pre-computation whenever the box size changes. This happens every +step for constant-pressure simulations.

Restrictions: none

diff --git a/doc/kspace_modify.txt b/doc/kspace_modify.txt index 19c91d3a42..47c17e04e9 100644 --- a/doc/kspace_modify.txt +++ b/doc/kspace_modify.txt @@ -114,10 +114,20 @@ The {diff} keyword specifies the differentiation scheme used by the PPPM method to compute forces on particles given electrostatic potentials on the PPPM mesh. The {ik} approach is the default. It performs differentiation in Kspace, but uses 3 FFTs to transfer the -computed fields back to real space. The analytic differentiation, or -{ad} approach uses only 1 FFT to transfer the computed fields back to -real space, but requires a somewhat larger PPPM mesh to achieve the -same accuracy as the {ik} approach. +computed fields back to real space (total of 4 FFTs per timestep). The +analytic differentiation, or {ad} approach uses only 1 FFT to transfer +the computed fields back to real space (total of 2 FFTs per timestep), +but requires a somewhat larger PPPM mesh to achieve the same accuracy +as the {ik} approach. + +IMPORTANT NOTE: Currently, only the {pppm} style supports the {ad} +option. Support from other {pppm} variants will be added later. + +IMPORTANT NOTE: If you run the {ad} option with a constant pressure +simulation (e.g. with "fix npt"_fix_nh.html), you may see a net +slow-down. This is because the {ad} option requires more expensive +pre-computation whenever the box size changes. This happens every +step for constant-pressure simulations. [Restrictions:] none