User`s guide

Using Model Output Plots to Validate and Compare Mod els
st≤ , and all avail able output s y(s),where
stk≤−
()
. The argument s
represents the data s ample number.
To make sure that the model picks up important dynam ic properties, let the
predicted time horizon kT be larger than the system time constants, where
T is the sampling interval.
Note Prediction with k=∞ means that no previous inputs are used in the
computation and prediction matches simulation.
To learn how to display simu lated or pre dicted outpu t, see t he d escription of
the plot settings in “How to Plot M odel Output Using the G U I” on page 8-11.
How to Plot Model Output Using the GUI
To create a mo del o u t pu t p lot f or parametric li n ear a nd nonlinear mod e l s in
the System Identification Tool GUI, select the Model output check box in
the Model Views area. For general information about creating and working
with plots, see “Working with Plots in the System Identificatio n Tool GUI” on
page 12-15.
To include or exclude a model on the plot, click the corresponding model icon
in the System Identification Tool G U I. Active models display a thick line
inside the Model Board icon.
The right side of the plot displays the percentage of the output that the model
reproduces (Best Fit), computed using the following equation:
Best Fit =−
−
−
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
×1 100
yy
yy
ˆ
In this equation, y is the measured output,
ˆ
y
is the sim u l ated or pred icted
model output, and
y
is th e me an of y. 100% corresponds to a perfect fit,
and 0% indicates that the fit is no better than guessing the output to be a
constant (
ˆ
yy=
).
8-11