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Re: Using Fourier and InverseFourier instead of Convolve

  • To: mathgroup at smc.vnet.net
  • Subject: [mg85986] Re: Using Fourier and InverseFourier instead of Convolve
  • From: "Dana DeLouis" <dana.del at gmail.com>
  • Date: Fri, 29 Feb 2008 06:28:12 -0500 (EST)

> dims[[1]]dims[[2]]-dims[[1]]+1)^((dims[[1]]-1)/2)....etc

Hi.  This does pretty much the same as your code, but uses a different
FourierParameters. 


LC[v_List] := Module[{r, c, m, signal},
   signal = FourierParameters -> {1, -1};
   {r, c} = Dimensions[v];
   m = PadRight[v, {r, r*c - r + 1}];
   m = Map[Chop[Fourier[#, signal]] &, m];
   m = Times @@ m;
   m = Chop[InverseFourier[m, signal]];
   If[MatrixQ[v, IntegerQ], Round[m], m]
   ] /; ArrayDepth[v] == 2



v = {{1, 2}, {3, 4}, {5, 6}};

LC[v]

{15, 68, 100, 48}

Fold[ListConvolve[#1, #2, {1, -1}, 0] &, First[v], Rest[v]]

{15, 68, 100, 48}


-- 
HTH   :>)
Dana DeLouis



"Solomon, Joshua" <J.A.Solomon at city.ac.uk> wrote in message
news:fq5qp3$l0s$1 at smc.vnet.net...
> First, let me thank all who responded to my query!
> Second, no, Daniel, your code works fine for me.
> Finally, FWIW here is code that does what I really wanted, which was to
> quickly convolve a long list of lists (each having the same length).
> Possibly not the most elegant code ever, but it works, as I said, FWIW:
> 
> cv[listOfLists_]:=With[{dims=Dimensions[listOfLists]},
>     (dims[[1]]dims[[2]]-dims[[1]]+1)^((dims[[1]]-1)/2)
>     InverseFourier[Times[##]]&@@(
>          Fourier[PadRight[#,dims[[1]]dims[[2]]-dims[[1]]+1]
>          ]&/@listOfLists)]
> 


<snip>




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