XVista manual page

NAME

fft1d - to Fourier-transform columnar data

SYNOPSIS

fft1d fname [ycol=] [icol=] [bias] [inverse] [num=] [step=] [verbose]

DESCRIPTION

fft1d performs the discrete Fourier transform on a file of ASCII data. The data must be arranged sequentially in rows; If "-" is specified for the file, the data are expected from stdin.

The program reads all the data in the input as a sequence of equally time spaced real values. If the number of points is not a power of two, then the data are padded with zeroes to make the next power of two. Lines that contain a `#' sign in the first column are skipped. You may use these lines for comments.

The transform is written to stdout; the frequency in column 1, the amplitude in column 2 and the phase (in degrees) in column 3.

OPTIONS

bias - subtracts the average of the existing data points from the input data before transformation.

complex - prints out the real and imaginary parts of the transform instead of the amplitude and phase.

icol - specifies the column in which the imaginary part of the input data are to be found. If icol is not specified the imaginary part of the input data is set to zero.

inverse - takes the reverse transform instead of the forward.

num - specifies the number data points to be used rather than the number of point read.

step - sets time interval between data points to be used in calculating the frequency. The default value is 1.0 second

verbose - prints out a number of diagnostic messages.

ycol - specifies the column in which the real part of the input data is to be found; the default is column one.