another example showing equivalence between multiplication of FFTs and conv

octave:17> a=[1 2]
a =

  1  2

octave:18> b=[3 4 9]
b =

  3  4  9

octave:19> conv(a,b)
ans =

   3  10  17  18

octave:20> A=fft([a 0 0])
A =

   3 + 0i   1 - 2i  -1 + 0i   1 + 2i

octave:21> B=fft([b 0])
B =

   16 +  0i   -6 -  4i    8 +  0i   -6 +  4i

octave:22> ifft(A.*B)
ans =

   3  10  17  18