FFT_IM(A) computes the imaginary part of Fast Fourier Transform of time series in variable A
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Arguments: |
A |
Variable with a regular time axis; may be a function of x, y, and/or z |
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Result Axes: |
X |
Inherited from A |
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Y |
Inherited from A |
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Z |
Inherited from A |
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T |
Generated by the function: frequency in cyc/(time units from A) |
The units of the returned time axis are "cycles/Dt" where Dt is the time increment.
Even and odd N's are allowed. N need not be a power of 2. FFT_RE and FFTP_IM assume f(1)=f(N+1), and the user gives the routines the first N pts.
Specifying the context of the input variable explicitly e.g.
LIST FFT_IM(A[l=1:58])
will prevent any confusion about the region. See the note in chapter 3 on the context of variables passed to functions.
The code is based on the FFT routines in Swarztrauber's FFTPACK available at www.netlib.org. See the section on FFTA for more discussion. For further discussion of the FFTPACK code, please see the document, Notes on FFTPACK - A Package of Fast Fourier Transform Programs.