Name

sfft_apply, dfft_apply, cfft_apply, zfft_apply − Application step for fast fourier transform in one dimension

FORMAT

Real transform: status = {S,D}FFT_APPLY (input_format, output_format, direction, in, out, fft_struct, stride)

Complex transform in complex data format: status = {C,Z}FFT_APPLY (input_format, output_format, direction, in, out, fft_struct, stride)

Complex transform in real data format: status = {C,Z}FFT_APPLY (input_format, output_format, direction, in_real, in_imag, out_real, out_imag,
 fft_struct, stride)

Arguments

input_format, output_format
character∗(∗)
Identifies the data type of the input and the format to be used to store the data, regardless of the data type.  For example, a complex sequence can be stored in real format.

The character ’R’ specifies the format as real; the character ’C’ specifies the format as complex. As convenient, use either upper- or lowercase characters, and either spell out or abbreviate the word. 

The following table shows the valid values:

For complex transforms, the type of data determines what other arguments are needed. When both the input and output data are real, the complex functions store the data as separate arrays for imaginary and real data so additional arguments are needed.  See the DXML Reference Manual’s chapter on "Using the Signal Processing Subprograms" for an explanation of real and complex data format. 

directioncharacter∗(∗)
Specifies the operation as either the forward or inverse transform. Use ’F’ or ’f’ to specify the forward transform. Use ’B’ or ’b’ to specify the inverse transform.

in, outreal∗4 | real∗8 | complex∗8 | complex∗16
Both the arguments are one-dimensional arrays.  The input and output arrays can be the same array. The IN array contains the data to be transformed. The OUT array contains the transformed data. The size of the output array is determined by the value of n provided to the _INIT function. 

in_real, out_real, in_imag, out_imag
real∗4 | real∗8
Use these arguments to perform a complex transform on real data format and storing the result in a real data format.

fft_structrecord /dxml_s_fft_structure/ for single-precision real operations
record /dxml_d_fft_structure/ for double-precision real operations
record /dxml_c_fft_structure/ for single-precision complex operations
record /dxml_z_fft_structure/ for double-precision complex operations
The argument refers to the structure created by the _INIT routine.

strideinteger∗4
Specifies the distance between consecutive elements in the input and output arrays, depending on the value of stride_1_flag provided in the _INIT function. 

Description

The _FFT_APPLY routines perform the fast Fourier transform of one-dimensional data, in either the forward or backward direction.  These routines are the second step of a three-step procedure.  The _FFT_APPLY routine computes the fast forward or inverse Fourier transform, using the internal data structures created by the _FFT_INIT subroutine. 

Use the _APPLY routines with their corresponding _INIT and _EXIT routines.  For example, use SFFT_APPLY after the SFFT_INIT and end with the SFFT_EXIT routine. 

The SFFT_APPLY and DFFT_APPLY functions perform the Fourier transform of a real sequence (forward) or a complex sequence (inverse) into real sequence. 

The CFFT_APPLY and ZFFT_APPLY functions perform Fourier transforms of a complex sequence into a complex sequence, storing the output in either real or complex data format. However, the argument list depends on the data format of the output.  See <REFERENCE>(ins_outs_sec) for an explanation of real and complex data format. 

Return Values

0DXML_SUCCESS()

12DXML_INS_RES()

13DXML_BAD_STRIDE()

15DXML_BAD_DIRECTION_STRING()

16DXML_BAD_FORMAT_STRING()

18 (real transform only)
DXML_BAD_FORMAT_FOR_DIRECTION()

Examples

INCLUDE ’{file_location}DXMLDEF.FOR’
INTEGER∗4 N, STATUS
REAL∗8 A(1026), B(1026)
RECORD /DXML_D_FFT_STRUCTURE/ FFT_STRUCT
N = 1024
STATUS = DFFT_INIT(N,FFT_STRUCT,.TRUE.)
STATUS = DFFT_APPLY(’R’,’C’,’F’,A,B,FFT_STRUCT,1)
STATUS = DFFT_EXIT(FFT_STRUCT)

This FORTRAN code computes the forward, real FFT of a vector, a, with length of 1024. The result of the transform is stored in b in complex form. Note that the length of b is 1026 to hold 513 complex values.

INCLUDE ’{file_location}DXMLDEF.FOR’
INTEGER∗4 N, STATUS
COMPLEX∗8 A(1024), B(1024)
RECORD /DXML_C_FFT_STRUCTURE/ FFT_STRUCT
N = 1024
STATUS = CFFT_INIT(N,FFT_STRUCT,.TRUE.)
STATUS = CFFT_APPLY(’C’,’C’,’F’,A,B,FFT_STRUCT,1)
STATUS = CFFT_EXIT(FFT_STRUCT)

This FORTRAN code computes the forward, complex FFT of a vector a, with length of 1024. The result of the transform is stored in b in complex form.