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### min_modify command

Syntax:

    min_modify keyword values ...

- one or more keyword/value pairs may be listed

      keyword = linestyle or dmin or dmax or lineiter
        linestyle value = secant or scan
        dmin value = min
          min = minimum distance for line search to move (distance units)
        dmax value = max
          max = maximum distance for line search to move (distance units)
        lineiter value = N
          N = max number of iterations in a line search

Examples:

    min_modify linestyle scan dmin 0.001 dmax 0.2
    min_modify lineiter 5

Description:

This command sets parameters that affect the minimization algorithms. The various settings may effect the convergence rate and overall number of force evaulations required by a minimization, so users can experiment with these parameters to tune their minimizations.

The linestyle sets the algorithm used for 1d line searches at each outer iteration of the minimizer. The secant style uses two successive force/energy evaluations to create a parabola and pick its minimum as an estimate of the next iteration's 1d minimum. The scan style starts its 1d search at dmin and doubles the distance along the line at which the energy is computed until the minimum is passed. It continues only as far as dmax. Normally, the secant method should find more accurate 1d minimums in less iterations, but the scan method can be more robust.

The dmin and dmax settings are both used by the scan line search as described above. For the secant line search, only the dmin value is used to pick an initial point to begin the secant approximation.

The lineiter setting is used by the secant algorithm to limit its iterations. The smaller the setting, the more inaccurate the line search becomes. Nonlinear conjugate gradient is not thought to require high-accuracy line searches in order to converge efficiently.

Restrictions: none

Related commands:

min_style, minimize

Default:

The option defaults are linestyle = secant, dmin = 1.0e-5, dmax = 0.1, and lineiter = 10.