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05/09/2009 at 05:57PM PDT, ID: 24395379 | Points: 500
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FFT code issue

Asked by montu_12 in MatLab Programming Language

Hi guys,

I am having hard time to figure out the 8 point FFT algorithm, I am passing thie input array which is currect according to the requirement but my FFT algorithm is not working and not giving me right values

Please check my code and see - what am i doing wrong....

Please Help
Its urgent 
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x = 0:1:40;
t = 0:1:40;
 
phas1 = 0;
phas2 = (2*pi)*(1/8);
phas3 = (2*pi)*(2/8);
phas4 = (2*pi)*(3/8);    
phas5 = phas4;
 
i(1) = 0;
 
for i= 2:9
    x(i) = x(i - 1) + phas1;
end
 
for i = 10:17 
    x(i) = x(i - 1) + phas2;
end
 
for i = 18:25 
    x(i) = x(i - 1) + phas3;
end
 
for i = 26:33 
    x(i) = x(i - 1) + phas4;
end
 
for i = 34:41 
    x(i) = x(i - 1) + phas5;
end
 
 
for i = 1:41 
    x(i) = cos(x(i));
end
 
 
stem(t, x);
 
s = ones(1,8);
fft(s)
 
% Bit Reversal 
% To do Bit Reversal we need to Flip the array values     
 
temp = x(1);
x(1) = x(8);
x(8) = temp;
 
temp = x(2);
x(2) = x(7);
x(7) = temp;
 
temp = x(3);
x(3) = x(6);
x(6) = temp;
 
temp = x(4);
x(4) = x(5);
x(5) = temp;
 
% Bit Reversal End
 
%%%%%%%% STAGE 1 %%%%%%%%%
 
x(1) = x(1) - x(2);
x(5) = x(2) + x(1);
 
x(3) = x(3) - x(4);
x(7) = x(4) + x(3);
 
x(2) = x(5) - x(6);
x(6) = x(6) + x(5);
 
x(4) = x(7) - x(8);
x(8) = x(8) + x(7);
 
 
%%%%%%%% STAGE 2 %%%%%%%%%
w = -0.707;
 
 
x(1) = x(1) - x(3);
x(5) = x(2) - x(4);
 
x(3) = x(3) + x(1);
x(7) = (x(4)* w) + x(2);
 
x(2) = x(5) - x(7);
x(6) = x(6) - x(8);
 
x(4) = x(7) + x(5);
x(8) = (x(8) * w) + x(6);
 
%%%%%%%% Stage 3 %%%%%%%%
 
x(1) = x(1) - x(5);
x(5) = x(2) - x(6);
 
x(3) = x(3) - x(7);
x(7) = x(4) - x(8);
 
x(2) = x(5) + x(1);
x(6) = (x(6)*w)  + x(2);
 
x(4) = (x(7) * w* w) + x(3);
x(8) = (x(8)* w *w *w) + x(4);
 
 
 
x(1)
x(2)
x(3)
x(4)
x(5)
x(6)
x(7)
x(8)
 
Keywords: FFT code issue
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[+][-]05/10/09 06:17 AM, ID: 24348248

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[+][-]05/10/09 04:33 PM, ID: 24350494

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