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MathGroup Archive 1999

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Simple recursive assignment

  • To: mathgroup at smc.vnet.net
  • Subject: [mg15996] Simple recursive assignment
  • From: "Peltio" <pelt.ioNOS at PAMiol.it>
  • Date: Fri, 19 Feb 1999 03:27:10 -0500
  • Organization: Peltio Inc.
  • Sender: owner-wri-mathgroup at wolfram.com

Can someone spare a little time for a trivial question?

The assignement
    a[0]=1.;
    a[1]=2.;
    a[n_]:=a[n]=a[n-1]-a[n-2]/n
works fine, all right...
    a[5]
        0.291667

But how can I achieve the same results when the expression a[n-1]-a[n-2]/n
is stored in a variable expr? The following approach leads to a Recursion
Limit error
    expr=b[n-1]-b[n-2]/n;

    b[0]=1;
    b[1]=2;
    b[n_]:=b[n]=expr

    b[3]
        $RecursionLimit::reclim: etc.

I tried a few combinations with Hold, Release, and so on but I can't fool
the recursion trap.I'm sure it's something trivial I'm missing
Any help would be greatly appreciated.
Thanks
Peltio,
peltioNO at SPAMusa.net

(remove NO SPAM to e-mail me)






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