User`s guide

3 Linear Model Identification
you increase the resolution in a specific frequency range, such as near a
resonance frequency. Conversely, you can m ake the frequency grid coarser in
the region where the noise dominates—at higher frequencies, for example.
Such customizing of the frequency grid assists in the estimation process by
achieving high fidelity in the frequency range of interest.
For
spafdr, the frequency resolution around the frequency k is the value R(k).
You can enter R(k) in any one of the following ways:
• Scalar value of the constant frequency resolution value in radians per
second.
Note The scalar R is inversely related to the M value used for etfe and
spa.
• Vector of frequency values the same size as the frequency vector.
• Expression using MATLAB workspace variables and ev aluates to a
resolution vector that is the same size as the frequency vector.
Thedefaultvalueoftheresolutionfor
spafdr is twice the difference between
neighboring frequencies in the frequency vector.
etfe Frequency Resolution for Periodic Input
If the input data is marked as periodic and contains an integer number of
periods (
data.Period is an integer), etfe computes the frequency response at
frequencies
2
12
πk
T
k
k
Period
where Period
()
= , ,...,
.
For periodic data, the frequency resolution is ignored.
Spectral Analysis Algorithm
You can estimate the frequency-response function of dynamic systems using
spectral analysis.
To better understand the spectral analysis algorithm, consider the following
description of a linear, dynamic system:
3-8