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MathGroup Archive 1999

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RE: Binomial eq..using FindRoot. Bug?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18061] RE: [mg17992] Binomial eq..using FindRoot. Bug?
  • From: "J.Guillermo Sanchez" <guillerm at gugu.usal.es>
  • Date: Tue, 15 Jun 1999 01:43:22 -0400
  • Delivery-date: Tue Jun 15 07:43:19 1999
  • References: <s75f9cdf.086@gwia.umsmed.edu>
  • Sender: owner-wri-mathgroup at wolfram.com

I post an e-mail for the mathgroup and I have received very nice solution.
Thanks every body.

But I have a curiosity.
My equation was:  Binomial[f n, r]/Binomial[n, r] == a.

If I resolve using FindRoot in the way,

h[n_,f_,a_]:= FindRoot[Binomial[f n, r]/Binomial[n, r] == a  , {r, 20}];
h[320,0.95,0.05].

Out: {r->53.3465}, that is OK

but if I move Binomial[n, r] to other side (the eq. is the same):

g[n_,f_,a_]:= FindRoot[Binomial[f n, r] == a Binomial[n, r] , {r, 20}];

g[320,0.95,0.05].

I recived the message:

FindRoot::"cvnwt":
    "Newton's method failed to converge to the prescribed accuracy after 15
iterations."

{r->14.5784} that is wrong.

It is a bug or are there any rules to use FindRoot that I didn't apply?.



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