difft1d(1)

PROGRAM
difft1d - Inverse 1D Discrete Fourier Transform.

SYNTAX

difft1d

-i  input data file (xviff file)

-o  resulting output file (xviff file)

[-c]
    select to center (0) or not to center (1) the transform

[-d]
    data processing direction (0 = down vectors, 1 = across bands)

[-s]
    scale fft by 1, 1/N or 1/sqrt(N):
    0 (Do not scale the output data),
    1 (Scale output data by 1/N),
    or 2 (Scale output data by 1/sqrt(N))
       [default = 0]

[-V]
    Gives the version for difft1d

[-U]
    Gives the usage for difft1d

[-P]
    Prompts for command line options

[-A [file1]]
    Creates the answer file called difft1d.ans or file1

[-a [file1]]
    Uses difft1d.ans or file1 as the answer file

DESCRIPTION
performs the 1D inverse Fourier transform on a set of data sequences. It can operate on Real and Complex data. NOTE: complex data is expected to be in rectangular (not polar) form. The output data type is VFF_TYP_COMPLEX.

The transform can be centered about its N/2 term by setting the -c option to 1. (The default setting is not centered.) If -c is set to 0, the transform will not be centered.

The output data can be scaled by 1/N or by 1/sqrt(N) if desired by using the -s option. The default setting is to leave the output data unscaled (-s = 0). If -s is set to 1, the output data is scaled by 1/N, where N in the number of points in the data sequence. The output can be scaled by 1/sqrt(N) by setting -s to 2.

The default data processing direction for difft1d is in the vector direction. This means that data stored in multiband format will be processed as a set of data sequences, where each sequence corresponds to a pixel location, and the points of each sequence are defined by the bands corresponding to that pixel location. The direction of processing can be changed so that each band is processed as a signal (instead of each vector being a signal) by setting the -d option to 1.

REQUIRED ARGUMENTS

-i  type: infile
    desc: input data file (xviff file)

-o  type: outfile
    desc: resulting output file (xviff file)

OPTIONAL ARGUMENTS

-c  type: boolean
    desc: select to center (0) or not to center (1) the transform
    default: false

-d  type: boolean
    desc: data processing direction (0 = down vectors, 1 = across bands)
    default: true

-s  type: integer
    desc: scale fft by 1, 1/N or 1/sqrt(N)
    allowed values:
    0 (Do not scale the output data),
    1 (Scale output data by 1/N),
    or 2 (Scale output data by 1/sqrt(N))

EXAMPLES

difft1d -i input_file -o output_file

difft1d -i input_file -o output_file -s 1
Computes the inverse FFT of input_file and scales the output by 1/N.

SEE ALSO
intro(1), verror(3), vgparms(3), vutils(3), ldifft1d(3)

RESTRICTIONS

COPYRIGHT
Copyright 1992, University of New Mexico. All rights reserved.