User's guide of Proceessing Modflow 5.0

Processing Modflow 143
while s and o are the scale and offset values for that parameter respectively. If you wish
to leave a parameter unaffected by scale and offset, enter the SCALE as 1.0 and the
OFFSET as 0.0.
< Group Definitions
Fig. 3.53 The List of Calibration Parameters (PEST) dialog box
In PEST, the input variables that define how derivatives are calculated pertain to parameter
groups rather than to individual parameters. These input variables are spcified in the Group
Definitions tab of the List of Calibration Parameters (PEST) dialog box.Thus derivative
data does not need to be entered individually for each parameter; however, if you wish, you
can define a group for every parameter and set the derivative variables for each parameter
separately. In many cases parameters fall neatly into separate groups which can be treated
similarly in terms of calculating derivatives.
- Number is the group number. The maximum number of paramter groups is 150.
- Description: A text describing the estimated parameter can be entered here (optional),
for example, “Transmissivity Group 1”. A maximum of 120 characters is allowed.
- INCTYP and DERINC: INCTYP defines the type of parameter increment
(perturbation) used for forward-difference calculation of derivatives with respect to any
parameter belonging to the group. INCTYP can be Relative, Absolute or Rel_to_max.
If it is Relative, the increment is calculated as a fraction of the current value of that
parameter; that fraction is specified in DERINC. If INCTYP is Absolute the parameter
increment is fixed at the value of DERINC and if INCTYP is Rel_to_max, the parameter
increment is calculated as a fraction of the group member with highest absolute value,
that fraction again being DERINC.
3.6.5 PEST (Inverse Modeling)