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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