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

568 HP MLIB User’s Guide

SRC1FT/DRC1FT Real-to-complex one-dimensional FFT

For best performance, these subprograms require that l be a product of powers

of 2, 3, and 5, that is, of the form

where p, q, r ≥ 0 and where either l = 1 or l is even.

Usage Because it is common to use one data set length repetitively, these subprograms

have a separate initialization call such that the setup can be performed only

once for each different transform size. You will, therefore, always have at least

two call statements to the FFT subprogram, using the same working storage

array.vb

VECLIB:

INTEGER*4 l, iopt, ier

REAL*4 x(l+2), work(2*l)

CALL SRC1FT(x, l, work, iopt, ier)

INTEGER*4 l, iopt, ier

REAL*8 x(l+2), work(2*l)

CALL DRC1FT(x, l, work, iopt, ier)

VECLIB8:

INTEGER*8 l, iopt, ier

REAL*4 x(l+2), work(2*l)

CALL SRC1FT(x, l, work, iopt, ier)

INTEGER*8 l, iopt, ier

REAL*8 x(l+2), work(2*l)

CALL DRC1FT(x, l, work, iopt, ier)

Input x Array containing l real data points or the ﬁrst l/2+1

complex data points of a conjugate-symmetric complex

data set of length l, to be transformed.

For a forward real-to-complex transform, the i-th real

data point is stored in x(i), i = 1, 2, ..., l.

For an inverse complex-to-real transform, the real part

of the i-th complex data point is stored in x(2×i−1) and

the imaginary part of the i-th data point is stored in

x(2×i), i = 1, 2, ..., l/2+1.

Not used if iopt = −3.

l Number of data points, l > 0.

l 2