Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2006
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2006

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: NonlinearFit problem

  • To: mathgroup at smc.vnet.net
  • Subject: [mg66553] Re: NonlinearFit problem
  • From: "Scout" <Scout at nodomain.com>
  • Date: Sat, 20 May 2006 04:46:46 -0400 (EDT)
  • References: <e4ekoe$9fa$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

"Oliver Friedrich" <frixoli at qarcor.de>
news:e4ekoe$9fa$1 at smc.vnet.net...
> Hallo,
>
> I want to use the NonlinearFit algorithm to obtain the parameters of a
> lossy line. There is a model
>
> Cell[BoxData[
>    RowBox[{
>      SqrtBox[
>        FractionBox[
>          RowBox[{
>            RowBox[{"2", " ", "\[ImaginaryI]", " ", "f", " ", "L", " ",
> "\[Pi]"}], "+",
>            RowBox[{
>              SqrtBox["f"], " ",
>              SqrtBox[
>                RowBox[{"2", " ", "\[Pi]"}]], " ",
>              SubscriptBox["R", "skin"]}]}],
>          RowBox[{"G", "+",
>            RowBox[{"2", " ", "\[ImaginaryI]", " ", "C", " ", "f", " ",
> "\[Pi]"}]}]]], " ",
>      RowBox[{"Tanh", "[",
>        RowBox[{"1.`", " ",
>          SqrtBox[
>            RowBox[{
>              RowBox[{"(",
>                RowBox[{"G", "+",
>                  RowBox[{"2", " ", "\[ImaginaryI]", " ", "C", " ", "f",
> " ", "\[Pi]"}]}], ")"}], " ",
>              RowBox[{"(",
>                RowBox[{
>                  RowBox[{"2", " ", "\[ImaginaryI]", " ", "f", " ", "L",
> " ", "\[Pi]"}], "+",
>                  RowBox[{
>                    SqrtBox["f"], " ",
>                    SqrtBox[
>                      RowBox[{"2", " ", "\[Pi]"}]], " ",
>                    SubscriptBox["R", "skin"]}]}], ")"}]}]]}], "]"}]}]],
> "Output",
>  CellLabel->"Out[166]="]
>
> that describes the input impedance of a lossy line when shorted at the
> end. The line parameters to obtain are Rskin,L,G and C. f is the
> independant variable. I have data of the line of the form {{f1,Z1},
> {f2,Z2},...} where Z is of course complex.
> Unfortunately NonlinearFit seems to have problems with complex numbers
> since it returns with messages saying "Objective function isn't real
> at...".
> Does anyone knows how to fix NonlinearFit for complex numbers or any
> other numerical method that could solve my problem?.
>
> Thank you
> Oliver
>

Why not with Amplitude and/or  Phase of the complex expression?


  • Prev by Date: Re: Insulating data from code
  • Next by Date: Re: (Newbie question): New types of numbers
  • Previous by thread: Re: NonlinearFit problem
  • Next by thread: Insulating data from code