7.5 alter_elements

• type: action command.
• function: modify the value of a parameter for one or more elements
• sequence: must follow run_setup.
• Command syntax, including use of equations and subcommands, is discussed in 7.2.

• name — A possibly-wildcard-containing string giving the names of the elements to alter. If not specified, then one must specify type.
• item — The name of the parameter to alter.
• type — A possibly-wildcard-containing string giving the names of element types to alter. May be specified with name or by itself.
• exclude — A possibly-wildcard-containing string giving the names of elements to excluded from alteration.
• value, string_value — The new value for the parameter. Use string_value only if the parameter takes a character string as its value.
• differential — If nonzero, the new value is the predefined value of the parameter plus the quantity given with value.
• multiplicative — If nonozero, the new given value is the predefined value of the parameter times the quantity given with value.
• alter_at_each_step — If nonzero, the changes requested by the command are performed at each simulation step. Note that if differential or multiplicative are non-zero, then changes will accumulate. (A more conventional way to perform such variation is with vary_elements.)
• alter_before_load_parameters — If alter_at_each_step, by default the alteration takes place after any load_parameters commands are processed. If this control is non-zero, the alteration takes place before any load_parameters commands are processed.
• verbose — If nonzero, information is printed to the standard output describing what elements are changed.
• allow_missing_elements — If nonzero, then it is not an error if an element matching name does not exist. Normally, such an occurence is an error and terminates the program.
• allow_missing_parameters — If nonzero, then it is not an error if an element does not have the parameter named with item. Normally, such an occurence is an error and terminates the program.
• start_occurence, end_occurence — If nonzero, these give the starting and ending occurence numbers of elements that will be altered. N.B.: if wildcards are used, occurence number counting is for each set of identically-named elements separately, rather than for the sequence of matched elements.
• s_start, s_end — If non-negative, these give the starting and ending position limits for the end-of-element locations of elements to be altered.
• after — The name of an element. If given, the alteration is applied only to elements that follow the named element in the beamline.
• before — The name of an element. If given, the alteration is applied only to elements that precede the named element in the beamline.