On Fri, 2 Sep 2005, Patrick Wallace wrote:
> Tim:
>
>
> Give the appended version of sla_UE2PV a go. Changes:
>
> * Newton's method for solving Everhart & Pitkin expression (17) is
> now damped 50% first time through.
>
> * Number of iterations increased by 1 (for neatness as it was in fact
> stopping one iteration short of the stated number).
>
> The code correctly implements the Everhart & Pitkin procedure, but there
> is clearly some lingering scope for incipient instability. The damping
> fixes your example, but I wouldn't like to guarantee that the solution is
> universal.
>
I just tried it on all the comets in our observing database (only about
10 comets though) and they all converge fine.
Strangely if I calculate positions for Hale-Bopp (part of my perl test
suite) my Mac gives answers that are 0.1 arcsec off my linux system. I'm
not sure how big a problem that is (the code is the same) [or what the
correct answer is to that accuracy]
So from a small sample things look fine. I can commit your changes
whenever you give the go ahead.
--
Tim Jenness
JAC software
http://www.jach.hawaii.edu/~timj
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