Re: Using Fourier and InverseFourier instead of Convolve

*To*: mathgroup at smc.vnet.net*Subject*: [mg85875] Re: Using Fourier and InverseFourier instead of Convolve*From*: m.r at inbox.ru*Date*: Tue, 26 Feb 2008 07:47:12 -0500 (EST)*References*: <fpooi0$1cg$1@smc.vnet.net>

On Feb 23, 3:21=A0am, "Solomon, Joshua" <J.A.Solo... at city.ac.uk> wrote: > OK, I must admit that I do not understand everything ListConvolve does, bu= t > I get the convolution I need when I do > ListConvolve[list1, list2, {1, -1}, 0] > In particular, the output has the appropriate length: > Length[list1]+Length[list2]-1. > Now, I would like to get the identical using Fourier and InverseFourier. > Is this possible? What is the appropriate syntax? > j It's certainly possible: In[1]:= {m, n} = {100, 200}; {list1, list2} = RandomReal[{-10, 10}, #]& /@ {m, n}; In[3]:= Norm[ListConvolve[list1, list2, {1, -1}, 0] - Sqrt[m + n - 1] InverseFourier[ Fourier[PadRight[list1, m + n - 1, 0.]] Fourier[PadRight[list2, m + n - 1, 0.]]]] Out[3]= 2.5382019*10^-12 Maxim Rytin m.r at inbox.ru