7.50 optimization_variable

• type: setup command.
• function: defines a parameter of an element to be used in optimization.
• sequence: must follow optimization_setup and precede beam definition (bunched_beam or sdds_beam).
• N.B.: It is not possible to optimize an element if the element name starts with one of the following characters: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, ., +, or -. The reason is that elegant will attempt to make an SDDS parameter name containing the element name, and these characters are disallowed at the beginning of such a name.
• Command syntax, including use of equations and subcommands, is discussed in 7.2.

• name — The name of the element.
• item — The parameter of the element to be varied.
• lower_limit, upper_limit — The lower and upper limits allowed for the parameter. If these are equal, the range of the parameter is unlimited.
• differential_limits — If nonzero, then the lower and upper limits are being given relative to the initial value, rather than in absolute terms.
• step_size, fractional_step_size — Specifies the initial step size (“simplex” optimization ) or the grid size in this dimension (“grid” or “sample” optimization). If fractional_step_size is positive, it is used in place of step_size; in that case, the step size is determined by using the indicated fraction of the difference between upper_limit and lower_limit.
• disable — If nonzero, the variable is ignored.
• force_inside — If nonzero, the initial value is forced inside the allowed range defined by the lower_limit and upper_limit parameters.
• no_element, initial_value — Allows defining a variable that is not connected to a beamline element, and giving the initial value for the variable. The variable can them be used in other optimization-related commands, e.g., optimization_covariable.