On Wed, Jan 21, 2009 at 10:06 AM, Brian Gough <[email protected]> wrote: > At Mon, 19 Jan 2009 18:20:56 -0500, > Liam Healy wrote: >> Is possible to change GSL to allow f & df _or_ fdf instead of "and", >> say providing a null pointer for the unneeded function. If that's >> already the case, can the documentation be made clear? > > Hello, > > To keep things simple using a NULL pointer is not supported -- the > recommended way is to make a small function fdf which calls f and df. > >> In a related puzzle, I find this statement about fdf hard to understand: >> "This function provides an optimization of the separate functions for >> f(x) and g(x)—it is always faster to compute the function and its >> derivative at the same time. " >> The user is providing the function, so whether it's an optimization or >> not depends on how it's written. It seems like an overstatement that >> it's "always" faster to compute the function and its derivative at the >> same time; I'm willing to believe it's (essentially) at least as fast >> perhaps. > > I was thinking that for analytic functions, at least, the function and > the derivative always have some terms in common so it is faster to > compute them together.
This has certainly been true in my experience. But then why is it necessary to supply f and df separately? Why not just have fdf as a single argument? What happens if f and/or df are not consistent with the corresponding values set by fdf? Liam > -- > Brian Gough > _______________________________________________ Help-gsl mailing list [email protected] http://lists.gnu.org/mailman/listinfo/help-gsl
