Program:      FFT

Purpose:      This program does a two-dimensional Fast Fourier Transform
              on a (pair of) map(s). Maximum map size is 2048 x 2048.

Category:     MANIPULATION

File:         fft.c

Author:       K.G. Begeman

Keywords:

   RINSET=    set and subset(s) input map(s) which contain the real part
              or the amplitude. Maximum number of maps is 2048.

   IINSET=    set and subsets(s) input map(s) which contain the imaginairy
              part or phase [no imaginairy part].

   ROUTSET=   set and subset(s) output map(s) which will contain the real
              part or amplitude.

   IOUTSET=   set and subset(s) output map(s) which will contain the
              imaginairy part or phase [no imaginairy part].
              

** SIGN=      sign of transform (1 or -1). If it is not clear from
              the number of input and output sets, this keyword
              will appear.
              Example:
                1 input set, 1 output set   ---> SIGN=+1 (for AP's)
                1 input set, 2 output sets  ---> SIGN=-1
                2 input sets, 1 output set  ---> SIGN=+1
                2 input sets, 2 output sets ---> will be asked

              SIGN=-1     sky to visibility
              SIGN=+1     visibility to sky

** PHASE=     input/output maps in amplitude and phase [Y]?
              Note that if only one input/output set is wanted, it is
              assumed by this program that the input/output set
              is COS and the SIN part is zero.

** VALUE=     Replace BLANKs in input sets by value [0.0].

Notes:        1) This program can only handle maps where the number
                 of pixels in X and Y are a power of two! The minimum
                 map size this program can handle is 16x16.
              2) This program is optimized for real to complex or
                 complex to real transforms.
              3) The program tries to allocate as much memory as needed.
                 If the allocation fails, it will create a scratch file.

Updates:      Aug 23, 1992: KGB, Document created.