B.3.5 Periodic Shadow Faces

Index:	18
Scheme symbol:	xf-periodic-face
C macro:	XF_PERIODIC_FACE
Status:	required only for grids with periodic boundaries

This section indicates the pairings of periodic faces on periodic boundaries. Grids without periodic boundaries do not have sections of this type. The format of the section is as follows:

      (18 (first-index last-index periodic-zone shadow-zone)(
      f00 f01
      f10 f11
      f20 f21
      .
      .
      .
      ))

where

first-index	=	index of the first periodic face pair in the list
last-index	=	index of the last periodic face pair in the list
periodic-zone	=	zone ID of the periodic face zone
shadow-zone	=	zone ID of the corresponding shadow face zone

These are in hexadecimal format. The indices in the section body ( f*) refer to the faces on each of the periodic boundaries (in hexadecimal), the indices being offsets into the list of faces for the grid.

Note:   In this case, first-index and last-index do not refer to face indices. They refer to indices in the list of periodic pairs.

Example:

      (18 (1 2b a c) (
      12 1f
      13 21
      ad 1c2
      .
      .
      .
      ))