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 https://www.netlib.org/. See the section on FFTA for more discussion.