Parameter Adjustment Controls Pane

The Parameter Adjustment Controls pane is on the PEST Properties dialog box under Control Data.

The variables specified on the Parameter Adjustment Controls pane are described in the PEST User Manual, Part I, Sections 4.2.7, 3.4.8, and 3.4.5. More extensive descriptions of these variables are in the PEST user manual.

RELPARMAX is the maximum relative change that a parameter is allowed to undergo between optimisation iterations. The relative change is defined as (bi-1 - bi )/bi-1. RELPARMAX must be greater than zero. See also PARCHALIM in the Manage Parameters dialog box.

FACPARMAX is the maximum factor change that a parameter is allowed to undergo. The factor change is defined as bi-1/bi or bi/bi-1 depending on whether bi-1 or bi is higher. FACPARMAX must be greater than 1. See also PARCHALIM in the Manage Parameters dialog box.

FACORIG If the absolute value of a parameter falls below FACORIG times its original value, then FACORIG times its original value is substituted for the denominator of equation 4.2.4. For factor-limited parameters, a similar modification is introduced to equation 4.2.5. Thus the constraints that apply to a growth in absolute value of a parameter are lifted when its absolute value has become less than FACORIG times its original absolute value. However, where PEST wishes to reduce the parameter’s absolute value even further, factor-limitations are not lifted; nor are relative limitations lifted if RELPARMAX is less than 1. FACORIG is not used to adjust limits for log-transformed parameters. FACORIG must be greater than zero. A value of 0.001 is often suitable.

IBOUNDSTICK Operation of the IBOUNDSTICK variable is described in section 3.4.5 of the PEST User Manual. It can be used to reduce the number of model runs required per iteration by permanently freezing at their bounds parameters which have encountered their bounds and seem reluctant to move from there. If IBOUNDSTICK is supplied as zero, or omitted altogether, PEST’s handling of bounds is unchanged from its normal operation as described in section 3.4.4 of the PEST User Manual. However if it is set to n (where n is a positive integer), PEST will permanently “glue” a parameter to its upper or lower bound if that parameter has resided there for n optimization iterations. Once a parameter is “glued” to one of its bounds it will never move again, for PEST will no longer include this parameter in its upgrade vector calculations. Nor will it calculate derivatives with respect to this parameter, thus reducing the number of model runs required per iteration. Experience has shown that use of the IBOUNDSTICK variable is generally not advisable. Hence it should normally be omitted or set to zero.

UPVECBEND As described in section 3.4.5 of the PEST User Manual, if UPVECBEND is set to 1 (checked), PEST will not shorten the parameter upgrade vector to ensure that parameter factor, relative and absolute change limits are respected. Instead it will “bend” this vector to allow imposition of limits on pertinent parameters while allowing unrestricted upgrade of parameters that, according to the parameter upgrade vector, are not required to undergo changes in value which attract these limits. In normal PEST practice, UPVECBEND should be set to zero (unchecked) or omitted from the PEST control file altogether. Either option deactivates parameter upgrade bending.