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MathGroup Archive 2000

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Re: Limitation of ListCorrelate?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24818] Re: Limitation of ListCorrelate?
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Sun, 13 Aug 2000 23:49:43 -0400 (EDT)
  • References: <8n5itj$n1l@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

> ListCorrelate does allow for
> "arbitrary" overhangs at the edges of a list, but the
> overhangs must be elements of the original kernel - so
> they are not arbitrary at all.

The fourth possible entry in ListCorrelate may help, but it does not give
separate control over the overhangs at the two ends.

?ListCorrelate gives

ListCorrelate[ker, list, klist, {p1, p2, ... }] forms the correlation in
which list is padded at each end with cyclic repetitions of the pi.


Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"D. Orr" <nonlnr at yahoo.com> wrote in message news:8n5itj$n1l at smc.vnet.net...
> Does anyone know how to get ListCorrelate to work with
> a *variable* kernel?  It seems that ListCorrelate
> would be a very efficient way to code finite
> difference schemes for solving PDE's.  However, at the
> edge of the computational domain, one would often like
> to implement "dummy points" which effectively change
> the stencil or kernel.  ListCorrelate does allow for
> "arbitrary" overhangs at the edges of a list, but the
> overhangs must be elements of the original kernel - so
> they are not arbitrary at all.  In general, the finite
> difference kernel at the edges will not be equal to
> any of the elements of the interior kernel.  I hope
> I'm missing something here, otherwise this would
> appear to be a very severe limitation of
> ListCorrelate.
>
> Regards,
>
> D. J.
>
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