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From: Peter Teuben <teuben@astro.umd.edu>
To: "gsl-discuss@sourceware.org" <gsl-discuss@sourceware.org>
Cc: Patrick Alken <patrick.alken@Colorado.EDU>
Subject: Re: Robust linear least squares
Date: Sun, 12 May 2013 17:56:00 -0000	[thread overview]
Message-ID: <518FD7B4.8070100@astro.umd.edu> (raw)
In-Reply-To: <518D6E3B.8080503@colorado.edu>

Patrick
I agree, this is a useful option!

   can you say a little more here how you define robustness. The one I
know takes the quartiles Q1 and Q3 (where Q2 would
be the median), then define D=Q3-Q1 and only uses points between
Q1-1.5*D and Q3+1.5*D to define things like  a robust mean and variance.
Why 1.5 I don't know, I guess you could keep that a variable and tinker
with it.
For OLS you can imagine applying this in an iterative way to the Y
values, since formally the errors in X are neglibable compared to those
in Y. I'm saying iterative, since in theory the 2nd iteration could have
rejected points that should have
been part or the "core points".  For non-linear fitting this could be a
lot more tricky.

peter


On 05/10/2013 06:01 PM, Patrick Alken wrote:
> Hi all,
>
>   I just committed a significant chunk of code related to robust
> linear regression into GSL and mainly wanted to update the other
> developers and any other interested parties. The main idea here is
> that ordinary least squares is very sensitive to data outliers, and
> the robust algorithm tries to identify and downweight outlier points
> so they don't drastically affect the model. I think this is something
> that has been needed in gsl for a while.
>
>   I've been developing the code for a while and have been using it
> successfully in my own work, and also validated it pretty extensively
> against the matlab implementation. I still need to make some automated
> tests for it which I should get to next week.
>
>   In the meantime, the code is very usable and working so feel free to
> try it out.
>
> Patrick

  reply	other threads:[~2013-05-12 17:56 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-05-10 22:01 Patrick Alken
2013-05-12 17:56 ` Peter Teuben [this message]
2013-05-12 18:13   ` Dirk Eddelbuettel
2013-05-12 18:14   ` Patrick Alken
2013-05-24 19:23 Timothée Flutre
2013-05-24 20:12 ` Patrick Alken

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