- type: setup command.
- function: define parameters for time-dependent modulation of elements
- sequence: must follow run_setup.
- N.B.: if the ramped element is modeled with a matrix, a significant performance hit may be
seen. It is best to use symplectic variants of the elements, since these don’t invoke the matrix
- Command syntax, including use of equations and subcommands, is discussed in 7.2.
STRING name = NULL;
STRING item = NULL;
STRING type = NULL;
STRING expression = NULL;
STRING filename = NULL;
STRING time_column = NULL;
STRING amplitude_column = NULL;
long refresh_matrix = 0;
long differential = 1;
long multiplicative = 0;
long start_occurence = 0;
long end_occurence = 0;
double s_start = -1;
double s_end = -1;
STRING before = NULL;
STRING after = NULL;
long verbose = 0;
double verbose_threshold = 0;
STRING record = NULL;
long flush_record = 1;
N.B.: This command will produce unpredictable results when used with error_element,
alter_elements, and load_parameters (except when change_defined_values=1). It should work
properly with link_elements in turn-by-turn mode when the source element is modulated, but not when
the target element is modulated.
- name — A possibly-wildcard-containing string giving the names of the elements to modulate.
If not specified, then one must specify type.
- item — The name of the parameter to modulate.
- type — A possibly-wildcard-containing string giving the names of element types to modulate.
May be specified with name or by itself.
- expression — RPN expression for the modulation amplitude A. The value of the time is on
top of the stack.
- filename — Name of SDDS file from which to read modulation data, if expression is not
- time_column — Name of column in filename giving time data for the modulation table.
- convert_pass_to_time — By default, the mean arrival time of the beam is used to compute
the time value for computing the modulation amplitude. If the arrival time vales are offset
by CHANGE_T=1 on RFCA elements, this won’t work as desired. In that case, one can compute
the time from the pass number and the position of the element within the lattice.
- amplitude_column — Name of column in filename giving amplitude data for the
modulation. Together, time_column and amplitude_column define a function A(t).
- refresh_matrix — Frequently there is a matrix associated with an element even if tracking
through the element does not use the matrix. In this case, elegant doesn’t normally update
the matrix for the element as it modulates the element, since that may involve a significant
time penalty. If this parameter is set to a non-zero value, the matrix will be updated. For
elements that use a matrix for tracking, the matrix is always updated.
- differential, multiplicative — Determine how the amplitude function A(t) is used to obtain
the new value of the parameter. There are four cases
- differential=1, multiplicative=0: v(t) = v0 + A(t) (default).
- differential=0, multiplicative=0: v(t) = A(t).
- differential=1, multiplicative=1: v(t) = v0 + v0A(t).
- differential=0, multiplicative=1: v(t) = v0A(t).
- start_occurence, end_occurence — If nonzero, these give the starting and ending occurrence
numbers of elements that will be modulated. N.B.: if wildcards are used, occurrence number
counting is for each set of identically-named elements separately, rather than for the sequence of
- s_start, s_end — If non-negative, these give the gaving and ending position limits for the
end-of-element locations of elements to be modulated.
- after — The name of an element. If given, the modulation is applied only to elements that follow
the named element in the beamline.
- before — The name of an element. If given, the modulation is applied only to elements that
precede the named element in the beamline.
- verbose — If nonzero, information is printed to the standard output as changes are made. Use for
debugging only, since otherwise it may slow the simulation.
- verbose_threshold — If nonzero, verbose information is printed only when the fractional change
exceeds the given value.
- record — Gives a possibly incomplete filename to which will be written a record of the values of the
- flush_record — Gives the interval in steps at which to flush the record file. Higher values result in
less frequent updates to the record, but may improve performance.