Reflection and Repetition

An unsigned repetition count and an asterisk indicate repetition of a beam line member. An optional minus sign (-) prefix causes reflection, i.e. all elements in the subsequence are taken in reverse order. Sub-lines of reflected lines are also reflected, but on physical elements the reflection flag is ignored. The minus sign must precede any repetition count. Repetitions are expanded immediately when a line is read, so are reflections of anonymous beam lines. The result is a flat line referring to a sequence of named elements and/or beam lines. When the line is output, it has the form resulting from this expansion.

Example:

R:LINE=(G,H);
S:LINE=(C,R,D);
T:LINE=(2*S,2*(E,F),-S,-(A,B));
TWISS,LINE=T;

The three lines are stored as follows:

R:LINE=(G,H);
S:LINE=(C,R,D);
T:LINE=(S,S,E,F,E,F,-S,B,A);

When T is expanded, substitution is recursive:

1. Replace sub-line S:

   
   (C,R,D,C,R,D,E,F,E,F,D,-R,C,B,A)
   

2. Replace sub-line R:

   
   (C,G,H,D,C,G,H,D,E,F,E,F,D,H,G,C,B,A)
   

Note that the inner sub-line R is reflected together with the outer sub-line S.