User`s guide

Worst-Case Analysis 13
-33
manually adjust the nominal model parameter values according
to the results, then perform another analysis with VARY DEV
specified.
Gaussian distributions
Parameters using Gaussian distributions are changed by 3σ
(three times sigma) for the worst-case analysis.
YMAX collatin
g
function
The purpose of the YMAX collating function is often
misunderstood. This function does not try to maximize the
deviation of the output variable value from nominal. Depending
on whether HI or LO is specified, it tries to maximize or
minimize the output variable value itself at the point where
maximum deviation occurred during sensitivity analysis. This
may result in maximizing or minimizing the output variable
value over the entire range of the sweep. This collating function
is usually useful when you know the direction in which the
maximum deviation occurs.
RELTOL
During the sensitivity analysis, each parameter is varied
(multiplied) by 1+RELTOL where RELTOL is specified in a
.OPTIONS statement, or defaults to 0.001.
Sensitivit
y
anal
y
sis
The sensitivity analysis results are printed in the output file
(
.out). For each varied parameter, the percent change in the
collating function and the sweep variable value at which the
collating function was measured are given. The parameters are
listed in worst output order; for example, the collating function
was its worst when the first parameter printed in the list was
varied.
When the YMAX collating function is used, the output file also
lists mean deviation and sigma values. These are based on the
changes in the output variable from nominal at every sweep
point in every sensitivity run.