Re: Discrete Convolution

• To: mathgroup at smc.vnet.net
• Subject: [mg18974] Re: Discrete Convolution
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Tue, 3 Aug 1999 13:44:27 -0400
• Organization: Universitaet Leipzig
• References: <7nrddv\$i60@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```Hi Alister,

In[1]:=
?ListConvolve

"ListConvolve[ker, list] forms the convolution of the kernel ker with
list. \
ListConvolve[ker, list, k] forms the cyclic convolution in which the kth
\
element of ker is aligned with each element in list. ListConvolve[ker,
list, \
{kL, kR}] forms the cyclic convolution whose first element contains
list[[1]] \
ker[[kL]] and whose last element contains list[[-1]] ker[[kR]]. \
ListConvolve[ker, list, klist, p] forms the convolution in which list is
\
padded at each end with repetitions of the element p. ListConvolve[ker,
list, \
klist, {p1, p2, ... }] forms the convolution in which list is padded at
each \
end with cyclic repetitions of the pi. ListConvolve[ker, list, klist, \
padding, g, h] forms a generalized convolution in which g is used in
place of \
Times and h in place of Plus. ListConvolve[ker, list, klist, padding, g,
h, \
lev] forms a convolution using elements at level lev in ker and list."

in Mathematica 4.0

Hope that helps
Jens

Alister McAlister wrote:
>
> I want a function that mimics Matlab's "conv" function for doing a discrete
> convolution of two lists.
>
>  CONV Convolution and polynomial multiplication.
>     C = CONV(A, B) convolves vectors A and B.  The resulting
>     vector is length LENGTH(A)+LENGTH(B)-1.
>     If A and B are vectors of polynomial coefficients, convolving
>     them is equivalent to multiplying the two polynomials.
>
> I wrote the following, but is there a way of either of
> (1) speeding up the code by changing the algorithm ...
>       ignoring simple things like the multiple evaluations
>       of Length and so forth which I have left
>       in only for what I hope is clarity; or
> (2) Using a built in function (possibly connected with polynomials) to do
> the same thing?
>
> Mark R Diamond

```

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