FFT
Compute a fast Fourier transform (FFT) or inverse fast/nonuniform Fourier transform (IFFT/INFT) using an FFT study step and solver,
Syntax
model.sol(sname).create(fname,"FFT")
model.sol(sname).feature(fname).set(pname,pvalue)
Description
Operation feature. The following properties are accepted:
Table 6-33: Valid FFT Solver Properties.
Property
Values
Default
Description
addstatsol
on | off
off
Add stationary solution.
control
String
user
Set control for FFT solver by study.
fftderiv
sol | firstderiv | secderiv
sol
Use the solution or its first or second time derivative as the input for a forward FFT.
fftendf
double
1.0
Endpoint of frequency interval, only applicable when fftsteptypef = interval.
fftendtime
double
1.0
End time for the time interval in a forward FFT.
fftextend
on | off
on
For an inverse NFT/FFT, extend the input data samples by adding complex conjugate pairs.
fftfile
on | off
off
Store intermediate FFT data on disk.
fftinputdata
fftperiodic | fftnotperiodic | ffthalfperiodic
fftperiodic
Interpret the input data as periodic, not periodic, or half-periodic (antisymmetric). The first two options replaces the Boolean fftperiodic property in earlier version.
fftmaxfreq
double
10
Maximum output frequency in forward FFT.
fftoutorder
nat | sym
nat
Output order (natural or symmetric) of frequencies for forward FFT.
fftouttrange
double array
 
Output times for inverse NFT/FFT.
fftphaseinexpr
String
 
Expression for input phase function, can be expressed in terms of t, freq, and niterFFTin (if applicable).
fftphaseoutexpr
String
 
Expression for output phase function, can be expressed in terms of t, freq, and niterFFTout (if applicable).
fftphasetypein
none | fromexpr
none
Method for input phase function.
fftphasetypeout
none | fromexpr
none
Method for output phase function.
fftrealstore
on | off
on
Do not store negative frequencies for real input.
fftscaling
cont | discrete
cont
Use a discrete or continuous scaling for the Fourier transform.
fftstartf
double
0.0
Starting point of frequency interval, only applicable when fftsteptypef = interval.
fftstarttime
double
0.0
Start time for the time interval in a forward FFT.
fftsteptypef
allfreqs | interval
allfreqs
Method for selecting frequencies from range.
fftstoretimes
out | store
out
Store time steps taken by the solver (out) or output times stored in fftstoretrange (store).
fftstoretrange
String (vector of output times)
 
Output times for the inverse FFT if fftstoretimes is set to store.
ffttranstype
transfft | transifft
transfft (depends on type of FFT study step)
Type of FFT transformation: forward or inverse.
fftwinalpha
double
0.5
Window parameter for a Tukey window.
fftwincenterfw
double
0.5
Window center for a Gaussian window function in a forward FFT.
fftwincenterinv
double
50
Window center for a Gaussian window function in an inverse NFT/FFT.
fftwindev
double
1
Standard deviation for a Gaussian window function.
fftwincutoff
double
1.0
Cutoff fraction for window function in [0, 1].
fftwindowfw
on | off
off
Use window function in forward FFT.
fftwindowinv
on | off
off
Use window function in inverse NFT/FFT.
fftwinexpr
String
 
Expression for window function, can be expressed in terms of t, freq, niterFFTin, and niterFFTout (if applicable).
fftwinmaxfw
double
1
Maximum (end) value for window in forward FFT.
fftwinmaxinv
double
100
Maximum (end) value for window in inverse NFT/FFT.
fftwinminfw
double
0
Minimum (start) value for window in forward FFT.
fftwinmininv
double
0
Minimum (start) value for window in inverse NFT/FFT.
fftwintypefw
fromexpr | cutoff | rectangle | gauss | hamming | hanning | blackman | tukey
fromexpr
Method for window function in a forward FFT.
fftwintypeinv
fromexpr | cutoff | rectangle | gauss | hamming | hanning | blackman | tukey
fromexpr
Method for window function in an inverse NFT/FFT.
keeplog
on | off
off
Keep warnings in stored log.
linpmethod
sol | init
sol
Prescribe the input values using a solution or an initial expression.
linpsol
String
current
Solution that defines the input values for the FFT study step/FFT solver.
linpsoluse
String
current
Subsolution that defines the input value for the FFT study step/FFT solver.
linpstudy
String
current
Study that defines input values for the FFT study step.
punit
String
Hz
Frequency unit.
statmethod
init | sol
sol
For an added stationary solution, use a solution or initial expression.
statsol
String
 
Solution to use as an added stationary solution.
statsolnum
String
 
The solution number to use for the solution used as an added stationary solution.
statsoluse
a stored solution or current
current
Use the current solution or a stored solution as the added stationary solution.
statstudy
String
 
Study from which the added stationary solution is chosen.
statt
double
 
Time value at which the added stationary solution is chosen.
statmanualsolnum
integer
 
Solution number of the added stationary solution.
tunit
String
s
Time unit.
winpunit
unit
Hz
Frequency unit for window in an inverse NFT/FFT.
Example
Code for Use with Java
model.study("std2").create("tdfft", "TimeToFreqFFT");
model.study("std2").feature("tdfft").set("linpstudy", "std1");
model.study("std2").feature("tdfft").set("fftstarttime", "0.5");
model.study("std2").feature("tdfft").set("fftendtime", "2.0");
model.study().create("std3");
model.study("std3").create("fdfft2", "FreqToTimeFFT");
model.study("std3").feature("fdfft2").set("linpstudy", "std2");
 
...
 
model.sol("sol7").create("fft1", "FFT");
model.sol("sol7").feature("fft1").set("ffttranstype", "transfft");
model.sol("sol7").feature("fft1").set("fftstarttime", "0.5");
model.sol("sol7").feature("fft1").set("fftendtime", "2.0");
model.sol("sol7").feature("fft1").set("control", "tdfft");
 
...
 
model.sol("sol9").feature("fft1").set("ffttranstype", "transifft");
model.sol("sol9").feature("fft1").set("control", "fdfft2");
 
model.study("std3").feature("fdfft2").set("linpmethod", "sol");
model.study("std3").feature("fdfft2").set("linpstudy", "std2");
model.study("std3").feature("fdfft2").set("linpsol", "current");
model.study("std3").feature("fdfft2").set("linpsoluse", "current")
 
...
 
model.sol("sol2").feature("ft1").set("fftstarttime", "0.5");
model.sol("sol2").feature("ft1").set("fftendtime", "2.0");
model.sol("sol2").feature("ft1").set("fftperiodic", "off");
model.sol("sol2").feature("ft1").set("fftoutorder", "nat");
 
...
 
model.sol("sol2").feature("ft1").set("fftphase", "on");
model.sol("sol2").feature("ft1").set("fftwintypefw", "fromexpr");
model.sol("sol2").feature("ft1").set("fftwinexpr","(niterFFTin<5)*niterFFTin");
model.sol("sol2").feature("ft1").set("fftphasetypein", "fromexpr");
model.sol("sol2").feature("ft1").set("fftphaseinexpr", "5+i*2*niterFFTin");
model.sol("sol2").feature("ft1").set("fftphasetypeout", "fromexpr");
model.sol("sol2").feature("ft1").set("fftphaseoutexpr","2+i*4*niterFFTout");
Compatibility
The property fftperiodic has been replaced by the property fftinputdata since version 6.2.
The properties fftbwalgtype and fftmeasure from earlier versions are no longer available since version 5.2.
In version 5.2, the property fftwintype for the window type in earlier versions was replaced by fftwintypefw and fftwintypeinv for the window type for a forward FFT and for an inverse NFT/FFT, respectively.
In version 5.2, the property fftwindow for switching a window on and off in earlier versions was replaced by fftwindowfw and fftwindowinv for the window type for a forward FFT and for an inverse NFT/FFT, respectively.
In version 5.2, the property tlist for the input time range to a forward FFT in earlier versions was replaced by the properties fftstarttime and fftendtime for the start time and end time, respectively.