C.6. - fft.4
Fft.4
does a fast Fourier transform of the current data.
fn fft.4
fn fft.4 options
or
fn . .
With no arguments, you are prompted for the type of transform and
type of data in which you are interested.
If you are supplying complex
input data or asking for complex output data, the real part is stored
in the
x
data column and the imaginary part is stored in the
s
(error-bar) data column.
You also can supply options on the
command line.
Valid options are:
. |
: |
use same options as last time |
+f or -f |
: |
forward (or reverse) transform |
+r or -r |
: |
real (or complex) input data |
+o or -o |
: |
real (or complex) output |
+a or -a |
: |
take absolute value (or don't) |
+s or -s |
: |
take absolute value squared (or don't) |
+m or -m |
: |
sort and merge the data (or don't) |
+i or -i |
: |
interpolate input data (or don't) |
n=# |
: |
set number of points |
f=# |
: |
set from value for interpolation |
t=# |
: |
set to value for interpolation |
|
The default options are:
+fro -asmi n=npts f=first_x t=last_x
Here
npts,
first_x
and
last_x
refer to the
number of points and the range of the current data.
Interpolation,
if used, is by a cubic spline.
(See
spline.4
).
Naturally, points
in
x
must be equally spaced for the transform to make sense.
Transforming more points than the number of in-core points, as set
in the
$CPLOTHOME/cplot_config
or
$HOME/.cplot_init
file is extremely slow because of the large number of file accesses
required.
When entering options interactively, it is possible to turn on a verbose
mode that will show the status of the transform as it works through
the data.
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