long turns = 2048;
double x0 = 1e-6;
double y0 = 1e-6;
double x1 = 3e-4;
double y1 = 3e-4;
long grid_size = 6;
long lines_only = 0;
long spread_only = 0;
double nux_roi_width = 0.02;
double nuy_roi_width = 0.02;
double scale_down_factor = 2;
double scale_up_factor = 1.05;
double scale_down_limit = 0.01;
double scale_up_limit = 1e-4;
long scaling_iterations = 10;
long use_concatenation = 0;
long verbose = 0;
long order = 2;
STRING tune_output = NULL;
- turns — The number of turns to track. If zero, then the concatenated matrix is used instead
of tracking, and all other parameters of this command are irrelevant. The matrix method
doesn’t work well with all lattices. The order of the concatenated matrix is given by the
concat_order control in twiss_output.
- x0, y0 — The initial x and y amplitudes to use for determining the small-amplitude tunes.
- x1, y1 — The initial x and y amplitudes to user for determining the tune shifts. These values
should be small enough to ensure linearity in the tune shift.
- grid_size — Size of the grid of points in x and y.
- lines_only — If nonzero, then instead of a full set of grid_size2 particles, only two lines of
particles with x = 0 and/or y = 0 are tracked. In this case, no Axi *Ayj terms are computed
(except for i = 0 or j = 0). However, in addition to being faster, the results may be more
reliable, e.g., ∂νx∕∂Ay = ∂νy∕∂Ax may be more closely satisfied.
- sparse_grid — Deprecated. If nonzero, then instead of a full set of grid_size2 particles, a
sparse grid of particles is tracked. Will save time at the expense of inaccurate higher-order
terms. Not recommended.
- spread_only — Compute the tune spread only and don’t bother with the tune shift
coefficients. These tune spreads can be optimized and appear in the twiss output file under the
names nuxTswaLower, nuxTswaUpper, and similarly for the y plane. This is the recommended
way to reduce tune shift with amplitude, as the tune spread is more reliable than the
coefficients of the expansion. (Particles that get lost are automatically ignored in both types
- nux_roi_width, nuy_roi_width — Widths of the region of interest for x and y tunes. As
the grid is filled in, elegant finds the tune for each tracked particle on the grid. Successive
tune values are looked for in the region of the given width around the previous tune value.
This prevents jumping from the main tune peak to another peak, which can happen when
the tune spectrum has many lines.
- scale_down_factor, scale_up_factor, scale_down_limit,
scale_up_limit, scaling_iterations — These control automatic scaling of the amplitudes.
If elegant sees a tune shift larger than scale_down_limit it will decrease x0 (or y0) by the
factor scale_down_factor. If elegant sees a tune shift smaller than scale_up_limit it will
increase x0 (or y0) by the factor scale_up_factor. Suggestion: if you find yourself playing
with these values and the initial amplitudes in order to get reliable TSWA coefficients, try
just using the tune spread.
- verbose — If nonzero, information about the progress of the algorithm is printed to the
- use_concatenation — If nonzero, then tracks with the concatenated matrix instead of
element-by-element. The order of the concatenated matrix is given by the concat_order
control in twiss_output. The user should experiment with this option to see if the results
are reliable for a particular lattice.