       Re: FindFit and NormFunction (to find a best fit by medians)

• To: mathgroup at smc.vnet.net
• Subject: [mg91751] Re: FindFit and NormFunction (to find a best fit by medians)
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Sun, 7 Sep 2008 05:35:53 -0400 (EDT)
• References: <g9t6j5\$j5d\$1@smc.vnet.net>

```Hi,

thank you that you was so kind to post a complete working example,

sampledata =
Table[{t, 0.2*Random[] + (2 + 0.1*Random[])*t}, {t, 0, 10, 0.25}];

myNorm[lst : {__Real}] := Sqrt[Median[lst^2]]

FindFit[sampledata, a + b*x, {a, b}, x, NormFunction -> myNorm]

will avoid the rectn-error message.

Regards
Jens

Stern wrote:
> I'm trying to use FindFit to find a best linear fit using Medians rather
> than Mean
>
> At one time, I believe the following code worked (I used it in several
> places, and never noted it failing, but it hasn't been used in a while and I
> don't actually remember):
>
> FindFit[sampledata,a+b*x,{a,b},x,NormFunction->(Sqrt[Median[#^2]]&)]
>
> Now, Mathematica seems to pass unevaluated expressions to the NormFunction,
> causing Median o fail with a "rectn: Rectangular array of real numbers is
> expected at position 1" error.
>
> I would appreciate any guidance.
>
> Michael
>
>

```

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