dfft2b(3P) Sun Performance Library dfft2b(3P)NAMEdfft2b - compute a periodic sequence from its Fourier coefficients.
The DFFT operations are unnormalized, so a call of DFFT2F followed by a
call of DFFT2B will multiply the input sequence by M*N.
SYNOPSIS
SUBROUTINE DFFT2B(PLACE, M, N, A, LDA, B, LDB, WORK, LWORK)
CHARACTER * 1 PLACE
INTEGER M, N, LDA, LDB, LWORK
DOUBLE PRECISION A(LDA,*), B(2*LDB,*), WORK(*)
SUBROUTINE DFFT2B_64(PLACE, M, N, A, LDA, B, LDB, WORK, LWORK)
CHARACTER * 1 PLACE
INTEGER*8 M, N, LDA, LDB, LWORK
DOUBLE PRECISION A(LDA,*), B(2*LDB,*), WORK(*)
F95 INTERFACE
SUBROUTINE FFT2B(PLACE, [M], [N], A, [LDA], B, [LDB], WORK, LWORK)
CHARACTER(LEN=1) :: PLACE
INTEGER :: M, N, LDA, LDB, LWORK
REAL(8), DIMENSION(:) :: WORK
REAL(8), DIMENSION(:,:) :: A, B
SUBROUTINE FFT2B_64(PLACE, [M], [N], A, [LDA], B, [LDB], WORK, LWORK)
CHARACTER(LEN=1) :: PLACE
INTEGER(8) :: M, N, LDA, LDB, LWORK
REAL(8), DIMENSION(:) :: WORK
REAL(8), DIMENSION(:,:) :: A, B
C INTERFACE
#include <sunperf.h>
void dfft2b(char place, int m, int n, double *a, int lda, double *b,
int ldb, double *work, int lwork);
void dfft2b_64(char place, long m, long n, double *a, long lda, double
*b, long ldb, double *work, long lwork);
ARGUMENTS
PLACE (input)
Character. If PLACE = 'I' or 'i' (for in-place) , the input
and output data are stored in array A. If PLACE = 'O' or 'o'
(for out-of-place), the input data is stored in array B while
the output is stored in A.
M (input) Integer specifying the number of rows to be transformed. It
is most efficient when M is a product of small primes. M >=
0; when M = 0, the subroutine returns immediately without
changing any data.
N (input) Integer specifying the number of columns to be transformed.
It is most most efficient when N is a product of small
primes. N >= 0; when N = 0, the subroutine returns immedi‐
ately without changing any data.
A (input/output)
Real array of dimension (LDA,N). On entry, the two-dimen‐
sional array A(LDA,N) contains the input data to be trans‐
formed if an in-place transform is requested. Otherwise, it
is not referenced. Upon exit, results are stored in
A(1:M,1:N).
LDA (input)
Integer specifying the leading dimension of A. If an out-of-
place transform is desired LDA >= M. Else if an in-place
transform is desired LDA >= 2*(M/2+1) and LDA must be even.
B (input/output)
Real array of dimension (2*LDB, N). On entry, if an out-of-
place transform is requested B contains the input data. Oth‐
erwise, B is not referenced. B is unchanged upon exit.
LDB (input)
Integer. If an out-of-place transform is desired, 2*LDB is
the leading dimension of the array B which contains the data
to be transformed and 2*LDB >= 2*(M/2+1). Otherwise it is
not referenced.
WORK (input/output)
One-dimensional real array of length at least LWORK. On
input, WORK must have been initialized by DFFT2I.
LWORK (input)
Integer. LWORK >= (M + 2*N + MAX(M, 2*N) + 30)
6 Mar 2009 dfft2b(3P)
