time interval between fft1 and fft2

Question

john 2011-3-23

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/3812-time-interval-between-fft1-and-fft2

Hello to everyone,

In my program I have created two different functions to compute the 1-D and 2-D fft (Fast Fourier Transform) of an array A(4x4).Now, I want to compute the time interval regarding the time difference between the 2 routines.Does anybody knows how it must be done?

Thamks in advance

%%%%%%%%%%%Program%%%%%%%%%%%%%%%%%% % Read & plot & find spectrum of *.dat image function []=Program_3(); clc;echo off;close all; A=[30,31,12, 9, 17,12,25,10, 12, 8,17, 9, 31,12,26,22];

A=double(A);B=A; disp(A); image_depth=31;tones=8;

 value =1;
switch value
  case 1
    B=ampl_fft(A);
  case 2
    B=ampl_fft2(A);
end;
max_B=max(max(B));min_B=0;B=(B-min_B)*(image_depth/(max_B-min_B));%back to image_depth
disp(round(B));

%==================================================================function [C]=ampl_fft(A) x=size(A,1);y=size(A,2); %/*-------- 2D - FFT ---------*/ %/*---------- do rows first ----------*/ C=A; for i=1:x, for j=1:y, if ( rem((i+j),2) == 1) C(i,j) = -C(i,j); else C(i,j) = C(i,j); end;%if end;%j end;%i

for i=1:x for j=1:y, Cy(j)=C(i,j); end;%j Cy=fft(Cy,y); for j=1:y, C(i,j) = Cy(j); end;%j end;%of i %/*------ do columns next---*/ for j=1:y %for each column for i=1:x Cx(i)=C(i,j); end;%i Cx=fft(Cx,x); %/*----- Compute Log Amplitude -----*/ for i=1:x C(i,j) = round(10.0 * log(1+ abs(Cx(i)) )); end;%i end;%j

%================================================================ function [C]=ampl_fft2(A) x=size(A,1);y=size(A,2);

%/*-------- 2D - FFT ---------*/ for i=1:x; for j=1:y; if ( rem((i+j),2) == 1) A(i,j) = -A(i,j); else A(i,j) =A(i,j); end;%if end;%j end;%i C=fft2(A); C=round(10.0 * log(abs(C)+1)); %==========================================

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Answer 1

Rob Graessle 2011-3-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/3812-time-interval-between-fft1-and-fft2#answer_5642

在 MATLAB Online 中打开

When you say "time difference", do you mean the difference in execution time between the two routines?

tic
B=ampl_fft(A);
time1=toc;
tic
B=ampl_fft2(A);
time2=toc;
timeDifference=time2-time1; % Difference in execution time in seconds

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Answer 2

john 2011-3-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/3812-time-interval-between-fft1-and-fft2#answer_5662

Now I want to form my own routine DFT employing the following formula: F(k)=sumA(k),(from 0 to N-1) where A(k)=x(n)*exp(-j*2*pi*k*n/N). I want to use it in function ampl_fft, istead of fft

I would appreciate if someone could help Thanks