From e1d881b11c54ca628bb05af4d53506c9836c93cf Mon Sep 17 00:00:00 2001 From: athomps Date: Wed, 24 Sep 2014 00:48:02 +0000 Subject: [PATCH] Update minimization documentation to reflect line quadratic default git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@12533 f3b2605a-c512-4ea7-a41b-209d697bcdaa --- doc/min_modify.html | 26 +++++++++++++++----------- 1 file changed, 15 insertions(+), 11 deletions(-) diff --git a/doc/min_modify.html b/doc/min_modify.html index e052b633a4..d9298f9b69 100644 --- a/doc/min_modify.html +++ b/doc/min_modify.html @@ -49,8 +49,20 @@ highly overlapped atoms from being moved long distances (e.g. through another atom) due to large forces.

The choice of line search algorithm for the cg and sd minimization -styles can be selected via the line keyword. The default -backtracking search is robust and should always find a local energy +styles can be selected via the line keyword. +The default quadratic line search algorithm starts out using +the robust backtracking method described below. However, once +the system gets close to a local +minimum and the linesearch steps get small, so that the energy +is approximately quadratic in the step length, it uses the +estimated location of zero gradient as the linesearch step, +provided the energy change is downhill. +This becomes more efficient than backtracking +for highly-converged relaxations. The forcezero +line search algorithm is similar to quadratic. +It may be more efficient than quadratic on some systems. +

+

The backtracking search is 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 @@ -58,14 +70,6 @@ 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 contrast, the quadratic line search algorithm tries to -reduce the forces to zero, while guaranteeing that the energy -changes is not positive (uphill). For some systems, it may also -be more efficient than the backtracking algorithm by -requiring fewer energy/force evaluations. The forcezero -line search algorithm is similar to quadratic. -It may be more efficient than quadratic on some systems. -

Restrictions: none

Related commands: @@ -74,6 +78,6 @@ It may be more efficient than quadratic on some systems.

Default:

-

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

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