dfft2b
dfft2b - 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.
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(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(LDB,*), WORK(*)
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
#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);
-
* 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 immediately without changing any data.
-
* A (input/output)
-
Real array of dimension (LDA,N).
On entry, the two-dimensional array A(LDA,N) contains the input data to be
transformed 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).
-
* 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.
Otherwise, 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)