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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
# AFFTRX -- Forward fourier transform (real transform, complex output).
# The fourier transform of the real array A of length NPIX pixels is computed
# and the NPIX/2+1 complex transform coefficients are returned in the complex
# array B. The first element of array B upon output contains the dc term at
# zero frequency, and the remaining elements contain the real and imaginary
# components of the harmonics. The transformation may be performed in place
# if desired. NPIX must be a power of 2.
#
# N.B.: The Fortran 77 standard guarantees that a complex datum is represented
# as two reals, and that the first real in storage order is the real part of
# the complex datum and the second real the imaginary part. We have defined
# B to be a type COMPLEX array in the calling program, but FFA expects a
# REAL array containing (real,imag) pairs. The Fortran standard appears to
# guarantee that this will work.
procedure afftrx (a, b, npix)
real a[ARB] # data (input)
complex b[ARB] # transform (output). Dim npix/2+1
int npix
int ier
begin
# The following is a no-op if A and B are the same array.
call amovr (a, b, npix)
# Compute the forward real transform.
call ffa (b, npix, ier)
if (ier == 1)
call fatal (1, "afftrx: npix not a power of 2")
end
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