Topas input files give you a lot of flexibility in how to set refinements up. The opportunity of making choices does make them complex.

Some parameters might apply to the whole refinement, some to individual xdds and some to individual strs.

The “for xdds” and “for strs” constructs help you set up complex files.

Beware of using the “@” symbol in a “for” section of the file. If you use @ on a fractional coordinate within a “for xdds” loop then that coordinate will have a different independent parameter in each data set. Give the parameter a name like x_Cu1 instead.

If you have complex input files (e.g. multi histogram distortion mode refinements) you can put prms in the “for strs” section. They are then merged as the section is expanded. Alan says that its better practice to have these outside loops. e.g. you can put them just above the “for” sections.

[To be completed]