Rename k0 to curv_k0 in examples

[krystophny]

Also, VSCode removed some whitespaces automatically. Should be a trivial merge.

[zhucaoxiang]

Thanks for the contribution. It was forgotten when updating the cost function. Useful documentation can be found at https://princetonuniversity.github.io/FOCUS/curvature.pdf. The formula might be complicated. An easier way is to use

case_curv = 3
curv_k0 = max_curvature_you_want_to_minimize
curv_alpha = 1
curv_beta = 2

and it is encouraged to increase Nseg if you want to optimize curvature.

[krystophny]

Thank you, @zhucaoxiang ! I encountered another issue when switching from 3 to 4 or 5 coils per period in the w7x_std example. Coils seem to be overlapping between periods (here for 5). Is there a setting I missed to change?

[zhucaoxiang]

@krystophny Do you mind sending me your input file, so I can reproduce the "issue"? You can send it to me privately via caoxiangzhu@ustc.edu.cn