function y = mirror(X)  %IFFTR=length(X(1,:)); %計算列長L=length(X(:,1));if isreal(X(1,:))    X=X;else    X(1,:)=zeros(1,R);end    newvec=zeros(2*L,R);    newvec(1:L,:)=X;    newvec(L+1,:)=X(1,:);    newvec(L+2:2*L,:)=conj(flipud(X(2:L,:))); %flipud函數功能是取復共軛y=newvec;