From 52855de029ef53767ec3382eb0ed4733bcbcd06b Mon Sep 17 00:00:00 2001 From: sjplimp Date: Thu, 26 Feb 2009 00:17:27 +0000 Subject: [PATCH] git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@2604 f3b2605a-c512-4ea7-a41b-209d697bcdaa --- doc/min_modify.html | 31 ++++++++++++++++++++++++------- doc/min_modify.txt | 31 ++++++++++++++++++++++++------- 2 files changed, 48 insertions(+), 14 deletions(-) diff --git a/doc/min_modify.html b/doc/min_modify.html index 5865b14092..a50ba7a820 100644 --- a/doc/min_modify.html +++ b/doc/min_modify.html @@ -17,9 +17,11 @@

Examples: @@ -29,7 +31,7 @@ keyword = dmax

Description:

This command sets parameters that affect the energy minimization -algorithms. The various settings may effect the convergence rate and +algorithms. The various settings may affect the convergence rate and overall number of force evaluations required by a minimization, so users can experiment with these parameters to tune their minimizations. @@ -39,10 +41,25 @@ gradient or steepest descent) and an inner iteration which is steps along a one-dimensional line search in a particular search direction. The dmax parameter is how far any atom can move in a single line search in any dimension (x, y, or z). Thus a value of 0.1 in real -distance units means no atom will move further than 0.1 Angstroms in a -single outer iteration. This is typically set to avoid the -possibility than one atom will be moved through another due to strong -overlapping forces. +units means no atom will move further than 0.1 Angstroms +in a single outer iteration. This prevents highly overlapped atoms +from being moved long distances (e.g. through another atom) due to +large forces. +

+

The choice of line search algorithm can be selected via the line +keyword. The default backtracking search is very robust and should +always find a local energy minimum. However, it will "converge" when +it can no longer reduce the energy of the system. Individual atom +forces may still be larger than desired at this point, because the +energy change is measured as the difference of two large values +(energy before and energy after) and that difference may be smaller +than machine epsilon even if atoms could move in the gradient +direction to reduce forces further. +

+

By contast, the quadratic line search algorithm is often able to +reduce forces closer to 0.0. It may also be more efficient than the +backtracking algorithm by requiring fewer energy/force evaluations. +However, it may not be as robust for some problems.

Restrictions: none

@@ -52,6 +69,6 @@ overlapping forces.

Default:

-

The option defaults are dmax = 0.1. +

The option defaults are dmax = 0.1 and line = backtrack.

diff --git a/doc/min_modify.txt b/doc/min_modify.txt index cacb331a46..e59cac7ea1 100644 --- a/doc/min_modify.txt +++ b/doc/min_modify.txt @@ -13,9 +13,11 @@ min_modify command :h3 min_modify keyword values ... :pre one or more keyword/value pairs may be listed :ulb,l -keyword = {dmax} +keyword = {dmax} or {line} {dmax} value = max max = maximum distance for line search to move (distance units) + {line} value = {backtrack} or {quadratic} + value = style of linesearch to use :ule [Examples:] @@ -25,7 +27,7 @@ min_modify dmax 0.2 :pre [Description:] This command sets parameters that affect the energy minimization -algorithms. The various settings may effect the convergence rate and +algorithms. The various settings may affect the convergence rate and overall number of force evaluations required by a minimization, so users can experiment with these parameters to tune their minimizations. @@ -35,10 +37,25 @@ gradient or steepest descent) and an inner iteration which is steps along a one-dimensional line search in a particular search direction. The {dmax} parameter is how far any atom can move in a single line search in any dimension (x, y, or z). Thus a value of 0.1 in real -distance units means no atom will move further than 0.1 Angstroms in a -single outer iteration. This is typically set to avoid the -possibility than one atom will be moved through another due to strong -overlapping forces. +"units"_units.html means no atom will move further than 0.1 Angstroms +in a single outer iteration. This prevents highly overlapped atoms +from being moved long distances (e.g. through another atom) due to +large forces. + +The choice of line search algorithm can be selected via the {line} +keyword. The default backtracking search is very robust and should +always find a local energy minimum. However, it will "converge" when +it can no longer reduce the energy of the system. Individual atom +forces may still be larger than desired at this point, because the +energy change is measured as the difference of two large values +(energy before and energy after) and that difference may be smaller +than machine epsilon even if atoms could move in the gradient +direction to reduce forces further. + +By contast, the {quadratic} line search algorithm is often able to +reduce forces closer to 0.0. It may also be more efficient than the +backtracking algorithm by requiring fewer energy/force evaluations. +However, it may not be as robust for some problems. [Restrictions:] none @@ -48,4 +65,4 @@ overlapping forces. [Default:] -The option defaults are dmax = 0.1. +The option defaults are dmax = 0.1 and line = backtrack.