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