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SENSAN
11-3
files; SENSAN then reads the “observation value files” written by INSCHEK in order to
ascertain current model outcome values. Because SENSAN must run INSCHEK at least once
every time it runs the model, it is essential that the executable file inschek.exe reside either in
the current directory or within a directory cited in the PATH environment variable.
Before running SENSAN, you should check the integrity of all instruction files which you
supply to it by running INSCHEK yourself outside of SENSAN.
11.2.4 The Parameter Variation File
SENSAN’s task is to run a model as many times as a user requires, providing the model with
a user-specified set of parameter values on each occasion. As discussed above, the parameters
which are to be varied from model run to model run are identified on one or a number of
template files. The values which these parameters must assume on successive model runs are
provided to SENSAN in a “parameter variation file”, an example of which is presented
below.
dep1
1.0
2.0
1.0
1.0
1.0
1.0
dep2
10.0
10.0
11.0
10.0
10.0
10.0
res1
5.0
5.0
5.0
6.0
5.0
5.0
res2
2.0
2.0
2.0
2.0
3.0
2.0
res3
10.0
10.0
10.0
10.0
10.0
11.0
Example 11.1 A parameter variation file.
The file shown in Example 11.1 provides 6 sets of values for 5 parameters; the parameter
names appear in the top row. As usual, a parameter name must be twelve characters or less in
length. The same parameter names must be cited on template files provided to SENSAN. In
fact, if there is a naming discrepancy between the parameters cited in the parameter
variation file and those cited in the template files supplied to SENSAN, parameters cited in
the parameter variation file which are absent from any template file(s) will not be provided
with updated values from model run to model run. This will manifest itself on the SENSAN
output files as a total lack of sensitivity for some parameters named in the parameter variation
file. A comprehensive checking program named SENSCHEK (see below) has the ability to
detect such inconsistencies in the SENSAN input dataset. Hence SENSCHEK should always
be run prior to running SENSAN.
The second and subsequent rows of a parameter variation file contain parameter values for
SENSAN to use on successive model runs. A separate model run will be undertaken for each
such row. A parameter variation file can possess as many rows as a user desires; hence
SENSAN can be set up to undertake thousands of model runs if this is considered necessary
(as it may be in Monte Carlo simulation).
In many sensitivity analyses, a user is interested in the effect of varying parameters, either
individually or in groups, from certain “base” values. In such cases, parameter base values
should appear on the second line of the parameter variation file immediately under the
parameter names. As will be discussed below, SENSAN produces two output files in which
variations from “base value outputs” are recorded, “base value outputs” being defined as
model outputs calculated on the basis of base parameter values.