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MathGroup Archive 2005

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NestList

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61391] NestList
  • From: "Dr A.H. Harker" <a.harker at ucl.ac.uk>
  • Date: Tue, 18 Oct 2005 02:44:32 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Dear All,

         I suspect I have missed something, but what I would really like is
a function similar to NestList, but where I can specify a function f that
takes more than one argument. Then, if at any step of the new function the
list of previous results is ll, whereas NestList will append to ll
f[ll[[-1]]], the new function would return f[ll[[-1]],ll[[-2]]...].

  Of course I can do this with the existing NestList, but as far as I can
see only by defining my f to work with a list {last,lastbutone,...}, in
which case I end up storing a lot of duplicate information in the
accumulated list.

  The particular application I have in mind is a simple finite difference
solution of the wave equation, where I might want to use NestList rather
than Nest so that I can animate the results. If the simulation involves two
spatial dimensions, storing duplicate copies of the information is a
significant problem. In fact in my application it's better to collect the
animation frames at rather lower frequency than they are calculated, to get
a reasonable compromise between accuracy and visual impact, so I tend not to
use NestList, but might this extension be useful in other areas. Or have I
just missed a clever trick?

 Tony Harker 
 Department of Physics and Astronomy
 University College London
 Gower Street
 LONDON
 WC1E  6BT
 (44)(0)207 679 3404
 a.harker at ucl.ac.uk




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