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###

A ``long'' FFT

**Compute FFT from the input QPOE file.
**

**input file: ***rp90_sti.qp*

**output files: ***rp90_ftp.tab, rp90_pwr.tab*

**In searching for short periods using a long data interval many bins are
necessary [(no. of bins) = **
**] and generation of a _ltc.tab file may prove
impractical. In such cases, the QPOE file may be input.
Only the largest Fourier coefficients, but not the complete
list of (***e.g.*,
**) coefficients should be used, so we set
power_thresh to exclude all but the largest from the table [root]_pwr.tab.
The normalization has been adjusted so the value of the power
coefficient, normpower, does not depend strongly on number of bins or number of
counts. A significant signal will have a value of **** for a
**10^{3}** bin transform and a value of **** for **10^{5}** bins.
Time required for a **10^{5}** bin transform is 2-3 minutes.
**

xt> fft.fftcoeff=no # don't generate a long list of coefficients
xt> fft.power_thresh=7 # set the significance threshold
xt> fft
input source file (table or time-sorted qpoe file): rp90_sti.qp
root name for output files [rrot_fft(ftp,pwr).tab]: rp90lng
background qpoe file: <cr>
input table column heading: src
number of bins 2048 # The task uses the closest power of 2 to the input value

**FFT done with 2048 bins!
** creating histogram output file rp90_ftp.tab
creating fft power output file rp90_pwr.tab

*rsdc@cfa.harvard.edu *

1998-06-10