On Thu, Dec 24, 2009 at 1:00 AM, Andrey Sisoyev
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