BOUNDARY TVD [{OFF | FACTOR factor} [ZONE range1[,range2[, ... rangen]] \
   [BOUNDARY {ALL | I1 | IMAX | J1 | JMAX | K1 | KMAX | OVERLAP}]]]

This keyword controls the TVD flux limiter in the explicit operator at the specified coupled boundaries. The same type of limiter (minmod, Koren, or van Albada) will be used as for the internal scheme.

FACTOR specifies the "compression" parameter for the TVD operator at the specified boundaries, which controls the amount of limiting. Larger numbers result in less limiting towards a first order operator. Setting factor to zero is equivalent to a first order operator, one corresponds to no overshoots, and two allows some increase in interface value over surrounding values.

The boundary TVD limiter must be more limiting than the interior TVD limiter for it to have any additional effect. I.e., the value factor must be less than the value used for the internal scheme.

In the zone specification, the range parameter(s) must be one of the following forms:

	zonenum		Selects zone zonenum
	begzone:endzone		Selects all zones from begzone to endzone
	begzone:		Selects all zones from begzone to MAXZONE, the total number of zones in the grid file
	:endzone		Selects all zones from 1 to endzone
	ALL		Selects all zones

By default, boundary TVD is on at all boundaries. If the BOUNDARY TVD keyword is not specified at all, the compression parameter will be the same as is used for the internal scheme. If BOUNDARY TVD is specified, but without additional keywords, the default value for factor will be used, as listed for the TVD keyword.

Note that if a particular zone (or zones) is to be specified, then either "OFF" or "FACTOR factor" must also be specified. And, if a particular boundary is to be specified, then the zone(s) must also be explicitly specified.

See Also: TVD