SYNOPSIS

fn fft.4 [options]

DESCRIPTION

The fft.4 function does a fast Fourier transform of the current data. With no arguments you are prompted for the type of transform and type of data you are interested in. 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 store in the s (error bar) data column.

You also can supply options to fft.4 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

Interpolation, if used, is by a cubic spline (see spline.4).

Transforming more points than the number of in-core points, as set in the $CPLOTHOME/cplot_config or $HOME/.cplot_init files, is extremely slow, due to the great 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.