Real transform: status = {S,D}FFT_GRP (input_format, output_format, direction, in, out, n, grp_size, lda, stride, grp_stride) Complex transform in complex data format: status = {C,Z}FFT_GRP (input_format, output_format, direction, in, out, n, grp_size, lda, stride, grp_stride) Complex transform real data format: status = {C,Z}FFT_GRP (input_format, output_format, direction, in_real, in_imag, out_real, out_imag, n, grp_size, lda, stride, grp_stride)
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: Subprogram Input Format Output Format Direction {S,D} 'R' 'C' 'F' 'C' 'R' 'B' 'R' 'R' 'F' or 'B' {C,Z} 'R' 'R' 'F' or 'B' 'C' 'C' 'F' or 'B' 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. direction character*(*) Specifies the operation as either the forward or inverse transform. Use 'F' or 'f' to specify forward transform. Use 'B' or 'b' to specify the inverse transform. in, out real*4 | real*8 | complex*8 | complex*16 Both arguments are two-dimensional arrays. The IN array contains the data to be transformed. The OUT array contains the transformed data. The IN and OUT arrays can be the same array. in_real, in_imag, out_real, out_imag real*4 | real*8 Use these arguments when performing a complex transform on real data format and storing the result in a real data format. n integer*4 Specifies the number of elements in the column within each one-dimensional data array; n > 0. For SFFT_GRP and DFFT_GRP, n must be even. grp_size integer*4 Specifies the number of one-dimensional data arrays; grp_size > 0. lda integer*4 Specifies the number of rows in two-dimensional data arrays; lda >= grp_size. Using lda = grp_size + {3 or 5} can sometimes achieve better performance by avoiding cache thrashing. stride integer*4 Specifies the distance between columns of active data arrays; stride >= 1. stride permits columns of IN and OUT arrays to be skipped when they are not part of the group. grp_stride integer*4 Specifies the distance between consecutive elements in a row in the IN and OUT arrays; grp_stride >= 1. grp_stride permits rows of IN and OUT arrays to be skipped when they are not part of the group.
The _FFT_GRP computes the fast forward or inverse Fourier transform on a group of one-dimensional data arrays. The transform is performed on the first row of elements of one-dimensional data arrays within the group. Data array can be skipped by setting the stride parameter. The transform then goes to the next row of elements. Similarly, rows of elements can be skipped by setting the grp_stride parameter. _FFT_GRP contrasts with the _FFT in that _FFT performs a transform on each element of a data array before going to the next data array. Although _FFT_GRP gives the same result as _FFT, _FFT_GRP is more efficient at completing the transform.
0 DXML_SUCCESS() 4 (real transforms only) DXML_ILL_N_IS_ODD() 8 DXML_ILL_N_RANGE() 12 DXML_INS_RES() 13 DXML_BAD_STRIDE() 15 DXML_BAD_DIRECTION_STRING() 16 DXML_BAD_FORMAT_STRING() 18 (real transforms only) DXML_BAD_FORMAT_FOR_DIRECTION()
INCLUDE 'CXMLDEF.FOR' INTEGER*4 N,GRP_SIZE REAL*8 A(100,514),B(100,514) N=512 LDA=100 GRP_SIZE=100 STATUS=DFFT_GRP('R','C','F',A,B,N,GRP_SIZE,LDA,1,1) This FORTRAN code computes a set of 100 FFT of size 512. The results of the transforms are stored in B in complex format. Note that the second dimension of A and B is 514 to hold the extra complex values (see the section on data storage).