[Haskell-cafe] ANNOUNCE: repr-0.3.2

[Lennart Augustsson]

Did you consider using the traced package?

2009/12/24 Bas van Dijk <v.dijk.bas at gmail.com>:
> On Thu, Dec 24, 2009 at 1:00 AM, Andrey Sisoyev
> <Andrejs.Sisojevs at nextmail.ru> wrote:
>> Where do you make use of it? :)
>
> A few months ago I was working on 'levmar'[1] a Levenberg-Marquardt
> data fitting library in Haskell. If you want your data fitting to be
> really fast you need to supply a Jacobian of the model function you
> want to fit. A Jacobian describes the partial derivatives of the
> parameters of the model function. I used Conal Elliott's
> vector-space[2] library to automatically derive a Jacobian from the
> model function.
>
> I was interested in the derivatives vector-space would come up with. A
> derivative however, is just a function so the only thing you can do
> with it is apply it to a value. This then yields a result which is
> usually just a Double. I wasn't really interested in this actual
> numeric result but more in the underlying numeric expressing that
> generated that result.
>
> So I wrote repr to visualize this numeric expression. However, after I
> wrote repr, the work on levmar stalled a bit and I did not actually
> get around to applying repr to the derivatives. I plan to make a new
> release of levmar in the coming weeks or so and I think I will use
> repr then.
>
> regards,
>
> Bas
>
> [1] http://hackage.haskell.org/package/levmar
> [2] http://hackage.haskell.org/package/vector-space
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