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发表于 2011-6-4 13:04:47
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希望對板主有用。
- function X = radix2(x,inverse)
- x = [1 1 1 1 0 0 0 0 ];
- inverse = 1;
- switch inverse
- case 1
- xcheck=x;
- p=nextpow2(length(x));
- x=[x zeros(1,(2^p)-length(x))];
- N=length(x);
- M=N/2; % Index Helping for Controlling range of indices of the Butterfly at Each Stage (Shrinking)
- for stage=1:log2(N); % No of times decimation has to occur
- for index=0:(N/(2^(stage-1))):(N-1); % Adjusting the index variations of the butterfly in each stage
- for n=0:M-1; % Within a stage, for a given index (single) as reference, develop a local Butterfly Index
- a=x(n+index+1)+ x(n+index+M+1);
- AA = exp((-j*(2*pi)/N)*(2^(stage-1))*(n));
- a = fi(AA);
- b=(x(n+index+1)- x(n+index+M+1)).* AA;
- x(n+1+index)=a;
- x(n+M+1+index)=b; % In place Computation
- end;
- end;
- M=M/2; % Used for creating Butterfly Pairs (INDEXing the wings) (Shrinkage)
- end;
- X=bitrevorder(x); % Bit reversing X[k] to obtain X[k] 0<k<N-1
- % Ycheck=fft(xcheck,N)
- % Cross Check the answer using inbuilt FFT
- case 2
- xcheck=x;
- x=x';
- p=nextpow2(length(x));
- x=[x zeros(1,(2^p)-length(x))];
- N=length(x);
- M=N/2; % Index Helping for Controlling range of indices of the Butterfly at Each Stage (Shrinking)
- for stage=1:log2(N); % No of times decimation has to occur
- for index=0:(N/(2^(stage-1))):(N-1); % Adjusting the index variations of the butterfly in each stage
- for n=0:M-1; % Within a stage, for a given index (single) as reference, develop a local Butterfly Index
- a=x(n+index+1)+ x(n+index+M+1);
- b=(x(n+index+1)- x(n+index+M+1)).*exp((-j*(2*pi)/N)*(2^(stage-1))*(n));
- x(n+1+index)=a;
- x(n+M+1+index)=b; % In place Computation
- end;
- end;
- M=M/2; % Used for creating Butterfly Pairs (INDEXing the wings) (Shrinkage)
- end;
- X=bitrevorder(x) ; % Bit reversing X[k] to obtain X[k] 0<k<N-1
- X = X'/N
- end
- % Ycheck=ifft(xcheck,N)
- % Cross Check the answer using inbuilt IFFT
- end
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