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# iFit/fft

## PURPOSE

c = fft(a) : computes the Discrete Fourier transform of iData objects

## SYNOPSIS

function b = fft(a, op, dim)

## DESCRIPTION

``` c = fft(a) : computes the Discrete Fourier transform of iData objects

@iData/fft function to compute the Discrete Fourier transform of data sets
using the FFT algorithm. The power spectrum density (PSD) is abs(fft)^2.
fft(a, 'ifft') is equivalent fo ifft(a)
fft(a, op, dim) and fft(a, dim) apply FFT or iFFT along dimension dim.

input:  a:   object or array (iData)
op:  can be 'fft' (default) or 'ifft' (inverse)
dim: dimension to apply FFT upon. dim=0 for all dimensions.
output: c: object or array (iData)
ex:     t=linspace(0,1,1000);
a=iData(t,0.7*sin(2*pi*50*t)+sin(2*pi*120*t)+2*randn(size(t)));
c=fft(a); plot(abs(c));

Version: Nov. 26, 2018

## CROSS-REFERENCE INFORMATION

This function calls:
• abs b = abs(s) : absolute value of iData object
• copyobj b = copyobj(s) : makes a copy of iData object
• diff b = diff(s) : computes the difference long 1st axis of iData object
• end b = end(s,index,n) : end value for iData objects
• fft c = fft(a) : computes the Discrete Fourier transform of iData objects
• get [...] = get(s, 'PropertyName', ...) : get iData object properties
• getalias [link, label,names] = getalias(s, 'AliasName') : get iData alias
• getaxis [val, lab] = getaxis(s, AxisIndex) : get iData axis value and label
• iData
• ifft c = ifft(a) : computes the inverse Discrete Fourier transform of iData objects
• interp [b...] = interp(s, ...) : interpolate iData object
• isempty isempty(s) : true for empty iData object
• isfield b = isfield(s, field) : check existence of field/alias in iData objects
• isnumeric b = isnumeric(s) : True for numeric iData object elements
• isscalar b = isscalar(s) : True for scalar iData objects
• max [m,id] = max(a,b, dim) : computes the maximum value of iData object(s)
• mean b = mean(s, dim) : mean value of iData object
• min [m,id] = min(a,b, dim) : computes the maximum value of iData object(s)
• ndims d = ndims(s) : get the dimensionality of iData object
• prod s = prod(a,dim) : computes the product of iData objects elements
• reshape c = reshape(a) : reshape the object Signal
• rmaxis s = rmaxis(s, Axis) : delete iData axes
• setalias [s,...] = setalias(s, AliasName, AliasLink, {AliasLabel}) : set iData aliases
• setaxis s = setaxis(s, rank, alias, value) : set iData axes
• size size(s) : get iData object size (number of elements)
• unique s = unique(a,dim) : set unique iData objects axes with no repetitions
• zeros s = zeros(s,N,M,P,...) : initialize an iData array
This function is called by:
• fft c = fft(a) : computes the Discrete Fourier transform of iData objects
• ifft c = ifft(a) : computes the inverse Discrete Fourier transform of iData objects

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