On Thu, Nov 17, 2022 at 5:29 PM Scott Ransom <sransom@nrao.edu> wrote:
A quick response from one of the leaders of a team that requires 80bit extended precision for astronomical work...
"extended precision is pretty useless" unless you need it. And the high-precision pulsar timing community needs it. Standard double precision (64-bit) values do not contain enough precision for us to pass relative astronomical times via a single float without extended precision (the precision ends up being at the ~1 microsec level over decades of time differences, and we need it at the ~1-10ns level) nor can we store the measured spin frequencies (or do calculations on them) of our millisecond pulsars with enough precision. Those spin frequencies can have 16-17 digits of base-10 precision (i.e. we measure them to that precision). This is why we use 80-bit floats (usually via Linux, but also on non X1 Mac hardware if you use the correct compilers) extensively.
Numpy is a key component of the PINT software to do high-precision pulsar timing, and we use it partly *because* it has long double support (with 80-bit extended precision): https://github.com/nanograv/PINT And see the published paper here, particularly Sec 3.3.1 and footnote #42: https://ui.adsabs.harvard.edu/abs/2021ApJ...911...45L/abstract
Going to software quad precision would certainly work, but it would definitely make things much slower for our matrix and vector math.
We would definitely love to see a solution for this that allows us to get the extra precision we need on other platforms besides Intel/AMD64+Linux (primarily), but giving up extended precision on those platforms would *definitely* hurt. I can tell you that the pulsar community would definitely be against option "B". And I suspect that there are other users out there as well.
Hi Scott, Thanks for sharing your feedback! Would you or some of your colleagues be open to helping maintain a library that adds the 80-bit extended precision dtype into NumPy? This would be a variation of Ralf's "option A." Best, Stephan
Scott NANOGrav Chair www.nanograv.org
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