On 4/15/08, Luc Maisonobe <[EMAIL PROTECTED]> wrote: > Niall Pemberton wrote: > > > the current code requires Java 1.6 to build. > > > > Yes, I missed that, thanks for reporting it. > > The reason is that several methods have been introduced in Math and > StrictMath as of java 6 (nextAfter, nextUp, scalb, copysign) and I use some > of them to implement their derivative. > > I have to find a way to either find a way to use an alternative > implementation and support them regardless of the version of java used to > build [nabla] itself, or use conditional compilation (using profiles > activated by jdk version in maven2) to include support for these functions > for derivatives only if they are available in the version of java used to > build [nabla]. > nextAfter is available in o.a.c.math.MathUtils and the others could easily be implemented, but IIUC what is going on here, the use is only required for manipulation of DifferentialPairs, not byte code analysis or differentiation per se (do I have this right?). Assuming that is correct, I would say the maven profile idea above should be OK.
I have a couple of comments / questions. 1. Some bigger picture documentation of how things work would make it easier for people to jump in and contribute. An example or two from the test classes in the xdocs would help with usage and an overview of how the automatic package works in either package javadoc, a Wiki page or xdoc somewhere would help. 2. This may be because I have not yet understood the big picture, but I wonder what differentiability really means here. What I mean is under what conditions do you know that nabla produces something that approximates what can reasonably be called a derivative and what happens at singularities or points where right- and left-hand derivatives both exist and are different. Looks like you made a decision in NablaMath.abs, for example, that assigns the right-hand value at 0. Why is this "correct"? The statement "differentiation can be computed even at domain boundaries" makes me worry about this. This can probably be gleaned from the literature on symbolic diff and I am just ignorant of it, but it would be good to get a recursive definition of the nabla differentiation operator and some theorems about its relationship to derivatives of recursive functions built from floating point primitives. Mabye some references in the overview? 3. I had a hard time keeping track of u0, u1 as property names in DifferentialPair. I am not sure what better names would be, but it might be good to think of better ones. More to come. I will add myself and fix a few typos and help with docs, etc. once I understand the code better. Phil --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
