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Re: lsqlin() error message

From: Olaf Till
Subject: Re: lsqlin() error message
Date: Sun, 7 Jul 2019 20:17:38 +0200
User-agent: NeoMutt/20170113 (1.7.2)

On Fri, Jul 05, 2019 at 05:16:54PM -0500, GoSim wrote:
> To the maintainer of optim:
> Best solution: remove lin. dependent rows and keep lsqlin working even if
> e.g. two of the same linear combinations are filled in.

I wouldn't think this could be done in a reasonable way. If you remove
a row, you remove the influence of one squared residual, i.e. the
influence of one element of 'D'.

> Second best solution: Do like Matlab but also write an error/warning so the
> user understands why he gets NaN. Lsqlin is very powerful and it is hard to
> understand that such a small thing can make it fail.

Sounds good to mee.

> Worst solution: just like Matlab
> Experimental solution: identify lin. dependent rows and to all but one of
> them add a very small white noise. The idea is that if you have many linear
> combinations that are the same this means something, it should be weighted.
> So by keeping them and adding a very small noise maybe the algorithm can
> handle it and it will be weighted.

I wouldn't try to guess within the optimizer function how to improve
the data. This is something which should be done, if at all, before
feeding the data into the optimizer, IMHO.


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