cscal2d,zscal2d(3F) cscal2d,zscal2d(3F)NAME
cscal2d, zscal2d - scales a 2D complex sequence.
SYNOPSYS
Fortran :
subroutine cscal2d( n1, n2, alpha, array, lda)
integer n1, n2, lda
real alpha
complex array(lda,n2)
subroutine zscal2d( n1, n2, alpha, array, lda)
integer n1, n2, lda
real*8 alpha
double complex array(lda,n2)
C :
#include <fft.h>
int cscal2d(int n1,int n2,float alpha,
complex *array,int lda);
int zscal2d(int n1,int n2,double alpha,
zomplex *array,int lda);
DESCRIPTIONcscal2d and zscal2d scale a 2D complex sequence of size N1xN2.
The Fourier Transforms are not normalized so the succession Direct-
Inverse transform scales the input data by a factor equal to the size of
the transform. So cscal2d or zscal2d may be used to scale back the
result.
PARAMETERS
N1 - Integer, the first dimension size of the 2D sequence.
Unchanged on exit.
N2 - Integer, the second dimension size of the 2D sequence.
Unchanged on exit.
Alpha - scaling floating point value.
ARRAY - Array containing the samples of the 2D sequence to be
transformed.
On input, the element {i,j} of the sequence is stored as A(i,j) in
Fortran , and A[i+j*lda] in C.
On exit, the array is overwritten by its transform. LDA - Integer,
leading dimension: increment between the samples of two consecutive sub-
sequences (e.g between {i,j+1} and {i,j}).
Unchanged on exit.
Example of Calling Sequence
Given a 2D complex sequence of size 64x1024. We successively apply a
Direct Fourier Transform, an Inverse Fourier Transform and finally scale
back the result by a factor 1/N (1/(64*1024.))-
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cscal2d,zscal2d(3F) cscal2d,zscal2d(3F)
This succession DirectFFT-InverseFFT-Scaling is equivalent to the
identity operator and the final sequence should be equal (with round-off
precision) to the initial sequence.
The offset between the first element of two succesive sub-sequence
(leading dimension) is 2049.
Fortran
complex array(0:2049-1,0:64-1), coeff(1024+64+2*15)
call cfft2di( 1024, coeff)
call cfft2d( -1, 1024, 64, array, 2049, coeff)
call cfft2d( 1, 1024, 64, array, 2049, coeff)
call cscal2d(1024,64,(1./real(1024*64)),array,2049)
C
#include <fft.h>
complex array[64*2049], *coeff;
coeff = cfft2di( 1024, NULL);
cfft2d( -1, 1024, 64, array, 2049, coeff);
cfft2d( 1, 1024, 64, array, 2049, coeff);
cscal2d( 1024,64,1./(float)(1024*64),array,2049);
NOTE_1 : The Direct and Inverse transforms should use opposite signs -
Which one is used (+1 or -1) for Direct transform is just a matter of
convention-
NOTE_2 : The Fourier Transforms are not normalized so the succession
Direct-Inverse transform scales the input data by a factor equal to the
size of the transform.
SEE ALSO
fft, cfft2di, zfft2di, cfft2d, zfft2d, cprod2d, zprod2d
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