Parameterise zoned parameters as an anchor value plus offsets

The additive counterpart of zone_ratio_param(), for quantities such as sediment temperature where a ratio is not meaningful (a ratio of degrees Celsius is arbitrary, and shallower zones are normally warmer than deeper ones). Zone 1 (the deepest) is calibrated directly and each shallower zone is the next deeper zone plus an offset: zone2 = zone1 + offset2, zone3 = zone2 + offset3. With lower >= 0 the values can only increase towards the surface; use a negative lower (or upper <= 0) to allow or force the opposite.

Usage

zone_offset_param(param, n_zones, lower = 0, upper = 5, start = 1)

Arguments

param: data.frame of parameters for a single zoned parameter. Either one row (the zone 1 value) or one row per zone. The row with index == 1 (or the first row if index is missing) is the anchor.
n_zones: integer; number of zones in the model for this parameter.
lower, upper: numeric; bounds for the offsets, in the units of the parameter.
start: numeric; starting value for the offsets when param has a single row. If param has one row per zone, starting offsets are derived from the zone values and clipped to the bounds.

Value

data.frame with the anchor row (index = 1) followed by n_zones - 1 offset rows.

Details

Offset rows are named <name>_zoffset and are converted back to per-zone values by expand_zone_ratios().

Examples

p <- data.frame(model = "glm_aed", file = "glm4.nml",
                name = "sediment/sed_temp_mean", value = 12, min = 5,
                max = 25, group = NA_character_, index = 1)
zone_offset_param(p, n_zones = 3, lower = 0, upper = 5, start = 1)
#>     model     file                           name value min max group index
#> 1 glm_aed glm4.nml         sediment/sed_temp_mean    12   5  25  <NA>     1
#> 2 glm_aed glm4.nml sediment/sed_temp_mean_zoffset     1   0   5  <NA>     2
#> 3 glm_aed glm4.nml sediment/sed_temp_mean_zoffset     1   0   5  <NA>     3