% Chapter 05: Example 5.23 High speed convolution
%
conv_time = zeros(1,150); fft_time = zeros(1,150);
%
for N = 1:150
    tc = 0; tf=0;
    L = 2*N-1; nu = round((log10(L)/log10(2))+0.45); L = 2^nu;
    for I=1:100
       h = randn(1,N);
       x = rand(1,N);
      t0 = clock; y1 = conv(h,x); t1=etime(clock,t0);
      tc = tc+t1;
      t0 = clock; y2 = ifft(fft(h,L).*fft(x,L)); t2=etime(clock,t0);
      tf = tf+t2;
    end
%
    conv_time(N)=tc/100;
    fft_time(N)=tf/100;
end
%
n = 1:150; subplot(1,1,1);
plot(n(25:150),conv_time(25:150),n(25:150),fft_time(25:150))
save times.txt conv_time fft_time -ascii -tabs