Contents
dfft2b - compute a periodic sequence from its Fourier coef-
ficients. 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(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);
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 chang-
ing 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) 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. 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 refer-
enced.
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)