User`s guide

1 Data Processing
Command
Description
Syntax Example
fft
Transforms time-domain
data to the frequency
domain.
You can specify
N,the
number of frequency
values.
To transform time-domain
iddata object t_data to
frequency-domain
iddata
object f_data with N
frequency points, use:
f_data =
fft(t_data,N)
ifft
Transforms
frequency-dom
ain data
to the time doma
in.
Frequencies a
re linear and
equally space
d.
To transform
frequency-dom
ain
iddata
object f_data t
o
time-domain
i
ddata
object t_data
,use:
t_data =
ifft(f_data)
Transforming Between Frequency-Domain and
Frequency-Response Data
You can transform frequency-response data to frequency-domain data
(
iddata object). The idf rd object represents comple x frequency-response of
the system at different frequencies. F or a descrip t ion of this type of data, see
“Importing Frequency-Response Data into MATLAB” on page 1-10.
When you select to transform single-input/single-output (SISO)
frequency-response data to frequency-domain data, the toolbox creates
outputs that equal the frequency responses, and inputs equal to 1. Therefore,
the ratio between the Fourier transform of the output and the Fourier
transform of the input is equal to the system frequency response.
For information about changing the frequency resolution of frequency-response
data to a n ew constant or variable (frequency-dependent) reso lution, see the
spafdr reference page. You might use this advanced feature to increase the
number of data points near the system resonance frequencies and m ake the
frequency vector coarser in the region outside the system dynam ics. Typically,
1-128