find_aperture

- type: setup/major action command.
- function: find the aperture in (x, y) space for an accelerator.

&find_aperture STRING output = NULL; STRING search_output = NULL; STRING boundary = NULL; STRING mode = "many-particle"; double xmin = -0.1; double xmax = 0.1; double ymin = 0.0; double ymax = 0.1; long nx = 21; long ny = 11; long n_splits = 0; double split_fraction = 0.5; double desired_resolution = 0.01; long assume_nonincreasing = 0; long verbosity = 0; long offset_by_orbit = 0; long n_lines = 11; long optimization_mode = 0; &end

`output`

-- The (incomplete) name of an SDDS file to send output to. Recommended value: ``%s.aper''.`mode`

-- May be ``many-particle'', ``single-particle'', ``one-line, ``three-lines'', or ``n-lines''. Many-particle searching is much faster than single-particle, but does not allow interval splitting to search for the aperture boundary. Both ``many-particle'' and ``single-particle'' modes involve searching from the outside inward, which improves speed but may result in including islands.The line modes avoid this by searching form the origin outward. Of these, the one-line and three-line modes are special: one-line mode searches the line from the origin to . three-line mode searches this line, plus the lines from the origin to and .

For n-line mode, the number of lines is set with the

`n_lines`

parameter. With , lines are explored from to , where takes values from to . In these modes, the output file contains a parameter called ``Area,'' which gives the area of the dynamic aperture.Also still recognized are other modes, namely, ``five-line'', ``seven-line'', ``nine-line'', and ``eleven-line''.

`search_output`

-- The (incomplete) name of an SDDS file for output of detailed information on each tracked particle (single-particle mode only). Recommended value: ``%s.apso''.`boundary`

-- The (incomplete) name of an SDDS file for the boundary points of the aperture search. Recommended value: ``%s.bnd''. Valid for many- and single-particle modes.`xmin`

,`xmax`

,`ymin`

,`ymax`

-- Region of the aperture search. The minimum values are relevant only for many- and single-particle modes.`nx`

-- For many- and single-particle modes, the number of x values to take in initial search. For line modes, this determines the initial x and y step sizes via and .`ny`

-- For many- and single-particle modes, the number of y values to take in search. Ignored for line modes.`n_splits`

-- If positive, the number of times to do interval splitting. Interval splitting refers to searching between the original grid points in order to refine the results. This is done only for single-particle and line modes.`split_fraction`

-- If interval splitting is done, how the interval is split.`desired_resolution`

-- If interval splitting is done, fraction of`xmax-xmin`

to which to resolve the aperture. Ignored for all but single-particle mode.`assume_nonincreasing`

-- If this variable is non-zero, the search assumes that the aperture at is no larger than that at . This results in tracking of fewer particles but may give a pessimistic result. Used only for single- and multi-particle modes.`offset_by_orbit`

-- A flag indicating whether to offset the transverse beam coordinates by the closed orbit before tracking. The default value is zero for backward compatibility, but the recommended value is 1.`verbosity`

-- A larger value results in more printouts during computations.`n_lines`

-- In ``n-lines'' mode, the number of lines to search.`optimization_mode`

-- If non-zero, then`find_aperture`

is a setup command and can be used with`elegant`'s internal optimizer. The quantity`Area`

is defined, giving the area of the dynamic aperture for use in the penalty function. This is available only for the line search modes.