Eliminating divisions in the `cel` routine

rodluger / Limbdark.jl

Analytical transit light curves for limb darkened stars

MIT License

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Eliminating divisions in the `cel` routine #48

Closed ericagol closed 6 years ago

ericagol commented 6 years ago

[x] Right now the recursive computation of elliptic integrals involves a square root and two divisions at each step in the iteration. I think that the divisions can be eliminated, which should further speed up cel and will help make the computation of the low-order limb-darkening faster.

ericagol commented 6 years ago

I was able to implement this in cel_bulirsch_nodiv, which does seem to work, and is faster than the prior version of cel_bulirsch. However, it appears to be numerically unstable, and causes NaN in some cases, so I'm scrapping this idea.

rodluger commented 6 years ago

Ah, too bad!

ericagol commented 6 years ago

There might be some way to get this to work, but I'm not sure it will provide sufficient speed-up to be worthwhile.