National Instruments 320571-01 用户手册

Computes the fast Hartley transform (FHT) of
the input sequence X.  The Hartley transform
of a function x(t) is defined as follows:

X(f)  = 

∫

-

∞

∞

 x(t) cas(2

π

ft) dt

where cas(x)  =  cos(x) + sin(x).

If Y represents the output sequence FHT {X} obtained via the FHT, then Y is obtained through the discrete
implementation of the Hartley integral:

Y

k

  = 

∑

i=0

n-1

 X

i

  cas 

( )

2

π

 ik

n

 ,

for  k = 0, 1, 2, … , n-1 .

where n is the number of elements in X.

X is a DSP Handle Cluster that indicates the memory buffer on the DSP board that contains the input
signal array.

Notes: The number of elements for the input array must be a power of two.

The operation is performed in place and the input array X  is overwritten by the output
FHT{X}.

The largest FHT that can be computed depends upon the amount of memory on your DSP
board.

FHT{X} is a DSP Handle Cluster that is identical to X, but with the results of FHT{X} already stored in
the memory buffer on the DSP board.

error in (no error) contains the error information from a previous VI.  If an error occurs, it is passed out
error out and no other calls are made.

error out contains the error information for this call.

The Hartley transform maps real-valued sequences into real-valued frequency domain sequences.  You can use it
instead of the Fourier transform to convolve signals, deconvolve signals, correlate signals, and find the power
spectrum.  Furthermore, you can derive the Fourier transform from the Hartley transform.

When the sequences to be processed are real-valued sequences, the Fourier transform produces complex-valued
sequences in which half of the information is redundant.  The advantage of using the Hartley transform instead of
the Fourier transform is that the Hartley transform uses half the memory to produce the same information the FFT
produces.  Further, the FHT is calculated in place and is as efficient as the Fourier transform.