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MathGroup Archive 1996

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FindRoot

  • To: mathgroup at smc.vnet.net
  • Subject: [mg4862] FindRoot
  • From: Ferruccio Renzoni <renzoni at fstgal03.tu-graz.ac.at>
  • Date: Thu, 26 Sep 1996 22:42:19 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Dear mathusers,

I have a doubt with FindRoot: I have a list of the kind { {xj,yj} }
and I want find the quantity "larghezza" using the following routines:

y0[l_List] := (Flatten @ Select[ l, Chop[#[[1]]] == 0. & ])[[2]]

meta[l_List] := Map[ #[[2]]&,l]

larghezza[y_List] := Module[{bl},
                     bl = Interpolation[y];
                     2 ( x /. FindRoot[ bl[x] ==
                     N[ (Max[meta[y]] + y0[y] )/2], {x,-.01,3.}] ) ]

Depending on the list examined this routine does not give me the correct answer.
I know that the answer is not correct because I can check it plotting the
list and extracting by eye the approximate answer.

Some idea? There are alternative commands to FindRoot?

Thanks in advance
Ferruccio Renzoni




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