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 property/values are accepted:

Table 6-32: Valid FFT Solver Property/Value Pairs
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.
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.
fftperiodic	on \| off	off	Periodicity of input data; only available if fftextend is set to off for inverse NFT/FFT (always available for forward 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	discrete	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 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.