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MathGroup Archive 2004

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Re: Re: NonlinearFit works not so good

  • To: mathgroup at smc.vnet.net
  • Subject: [mg49633] Re: [mg49587] Re: NonlinearFit works not so good
  • From: DrBob <drbob at bigfoot.com>
  • Date: Sun, 25 Jul 2004 02:55:37 -0400 (EDT)
  • References: <cdqqa4$kkd$1@smc.vnet.net> <200407240747.DAA05792@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

Omega Consulting's "Copy as InputForm" palette is very useful for making readable posts:

http://eclecticdreams.net/DrBob/copy_as_inputform.htm

The code in Kevin's post is the same as this:

p1 = Plot[100 Sin[3 x + 1] + 2, {x, 0, 5}];
data = p1[[1, 1, 1, 1]];
p2 = ListPlot[data];
f[a_, b_, c_, d_, x_] := a Sin[b  x + c] + d
lsfit[a_, b_, c_, d_] := Plus @@ Apply[ (f[a,
  b, c, d, #1] - #2)^2 &, data, {1}]
lsfit[100, 3, 0, 2]
sol = FindMinimum[lsfit[a, b, c, d], {a, 90, 91}, {b, 2.5, 2.6}, {c, 0,
     1}, {d, 0, 1}, MaxIterations -> 1000]
Plot[f[a, b, c, d, x] /. sol[[2]], {x, 0, 5}, Epilog -> {AbsolutePointSize[
       4], p2[[1]]}];

The exponent 2 in the definition of 'lsfit' caused all that unreadable junk!

Bobby

On Sat, 24 Jul 2004 03:47:17 -0400 (EDT), Kevin J. McCann <kmccann at umbc.edu> wrote:

> I am a simple kinda guy; so, I tend to use a "roll-your-own" LSQ whenever
> possible. I do this especially when I have a multivariate fit. The real
> problem is that it is that there is no single answer due to the periodicity
> of the sine. This makes a numerical search complicated. Anyway, here is my
> version.
>
> \!\(\*
>   RowBox[{\(p1 = Plot[100\ Sin[3\ x + 1] + 2, {x, 0, 5}];\),
>     "\n", \(data = p1[\([\)\(1, 1, 1, 1\)\(]\)];\),
>     "\n", \(p2 = ListPlot[data];\), "\n",
>     RowBox[{\(f[a_, b_, c_, d_, x_]\), ":=",
>       StyleBox[\(a\ Sin[b\ \ x + c] + d\),
>         FormatType->StandardForm]}],
>     "\n", \(lsfit[a_, b_, c_, d_]\  := \
>       Plus\  @@ Apply[\ \((f[a, b, c, d, #1] - #2)\)\^2 &, data, {1}]\),
>     "\n", \(lsfit[100, 3, 0, 2]\),
>     "\n", \(sol =
>       FindMinimum[
>         lsfit[a, b, c, d], {a, 90, 91}, {b, 2.5, 2.6}, {c, 0, 1}, {d, 0, 1},
>         MaxIterations \[Rule] 1000]\),
>     "\n", \(Plot[f[a, b, c, d, x] /. sol[\([\)\(2\)\(]\)], {x, 0, 5},
>         Epilog \[Rule] {AbsolutePointSize[4], p2[\([\)\(1\)\(]\)]}];\)}]\)
>
> Cheers,
> Kevin



-- 
DrBob at bigfoot.com
www.eclecticdreams.net


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