find_aperture

• type: 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;
&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-line'', ``five-line'', ``seven-line'', ``nine-line'', or ``eleven-line''. 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 n-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 $(x_{max}, y_{max})$. three-line mode searches this line, plus the lines from the origin to $(x_{max}, 0)$ and $(0, y_{max})$. For $n$-line modes with $n>3$, $n$ lines are explored from $(0,0)$ to $(x_{max}*sin(\theta), y_{max}*cos(\theta))$, where $\theta$ takes values from $-pi/2$ to $\pi/2$. In these modes, the output file contains a parameter called ``Area,'' which gives the area of the dynamic aperture.

• 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 $\Delta x = x_{max}/n_x$ and $\Delta y = y_{max}/n_x$.
• 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 ${\rm y+sign(y)*\Delta y}$ is no larger than that at ${\rm y}$. 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.