octave:1> foo = pi*ones(1,1e7); octave:2> foof = fft(foo); octave:3> sum(foo) ans = 3.1416e+07 octave:4> foof(0) error: invalid vector index = 0 octave:4> foof(1) ans = 3.1416e+07 octave:5> sum(foo) - foof(1) ans = 0.0075805 octave:6> pi*1e7 - foof(1) ans = 0 octave:7> pi - 3.14159 ans = 2.6536e-06 octave:8> pi - 3.1415926536 ans = -1.0207e-11 octave:9> sum(foo) - pi*1e7 ans = 0.0075805