In order to conserve memory, it is possible to limit the computation space to only the right side of the x=0 axis. The left half is assumed to be the same as the right half.
If SYMMETRIC is selected, the field profile will be symmetric about x = 0 axis (even order modes).
If ANTI-SYMMETRIC is selected, the field profile will be antisymmetric about the x = 0 axis (odd order modes).
If ASYMMETRIC is selected, the entire computation space is used, and no symmetry is assumed.