The accelerator to be studied is known to OPAL as a sequence of
physical elements called a beam line. A beam line is built from
simpler beam lines whose definitions can be nested to any level. A
powerful syntax allows to repeat or to reflect pieces of beam lines.
Formally a beam line is defined by a
label see Section [label] gives a name to the beam line for later reference.
member may be one of the following:
An element label,
A beam line label,
A sub-line, enclosed in parentheses,
Beam lines can be nested to any level.
The simplest beam line consists of single elements:
Position vector of the origin of the line. All elements in this line that are placed using
ELEMEDGEuse this position as reference.
Vector of Tait-Bryan angles [bib:tait-bryan] of the orientation of the line at the origin.
Instead of referring to an element, a beam line member can refer to another beam line defined in a separate command. This provides a shorthand notation for sub-lines which occur several times in a beam line. Lines and sub-lines can be entered in any order, but when a line is used, all its sub-lines must be known.
This example produces the following expansion steps:
valuated to constants immediately.