[Haskell-cafe] ANNOUNCE: repr-0.3.2

[Bas van Dijk]

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