HP MLIB User's Guide Vol. 2 7th Ed.

Chapter 5 Fast Fourier Transforms 585
Simultaneous real-to-complex one-dimensional FFT CRCFTS/ZRCFTS
Output z The transformed data replaces the input if ier = 0 is
returned. Unchanged if ier < 0.
For a forward real-to-complex transform, each
transformed data set satisfies the conjugate-symmetry
condition.
For an inverse complex-to-real transform, the real
result is stored in the real parts of z and the imaginary
parts of z are set to zero.
ier Status response:
ier = 0 Normal return—transform successful.
ier = −1 l ≤ 0.
ier = −2 incl ≤ 0.
ier = −3 n ≤ 0.
ier = −4 incn ≤ 0.
ier = −5 l, incl, n, and incn are incompatible.
Refer to “Notes.”
Notes Typically, z is a two- or three-dimensional array with each set of data being a
one-dimensional section of the array, that is, all but one subscript is constant
within a data set.
If z is a two-dimensional array of dimension ldz by mdz, and if the data sets are
stored in the columns of z, then l ≤ ldz, n ≤ mdz, incl = 1, and incn = ldz. For
example, use
CALL CRCFTS (z, l, 1, n, ldz, iopt, ier)
If z is a two-dimensional array as above and the data sets are stored in the rows
of z, then l ≤ mdz, n ≤ ldz, incl = ldz, and incn = 1. For example, use
CALL CRCFTS (z, l, ldz, n, 1, iopt, ier)
If z is a three-dimensional array of dimension ldz by mdz by ndz, then incl and
incn will usually be 1, ldz, or ldz×mdz, depending on which of the subscripts of
the three-dimensional array varies within a data set, which subscript varies
between data sets, and which remains constant. Specifically, if the subscript
that varies within a data set is the
1st subscript, use incl = 1.
2nd subscript, use incl = ldz.
3rd subscript, use incl = ldz×mdz.