function f=ihwtdn(a)
%
% Copyrite(c) D.E.Newland 1992
% All rights reserved
%
N=length(a);
n=round(log(N)/log(2));
F(1)=a(1);F(2)=a(2);
for j=1:n-2
    F(2^j+1:2^(j+1))=fft(a(2^j+1:2^(j+1)))/2^j;
    F(N-2^(j+1)+2:N-2^j+1)=fliplr(ifft(fliplr(a(N-2^(j+1)+2:N-2^j+1))));
end
F(N/2+1)=a(N/2+1);
F(N)=a(N);
f=ifft(F)*N;