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[Octave-bug-tracker] [bug #48307] sinc loses precision for large argumen


From: Colin Macdonald
Subject: [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments
Date: Tue, 5 Jul 2016 04:14:17 +0000 (UTC)
User-agent: Mozilla/5.0 (X11; Fedora; Linux x86_64; rv:47.0) Gecko/20100101 Firefox/47.0

Follow-up Comment #22, bug #48307 (project octave):

> the lack of precision in the input, which is insurmountable.

Careful here.  I've said several times that is *not a given* that sinc must be
computed using the formula sin(x)/x.  One could search for an asymptotic
expansion for example in large x, or maybe do a contour integral with
quadrature in the complex plane.  The we use sin(x)/x for smallish x and
switch to that something else for large x.  Although I have not found anyone
who does this yet (Matlab and SciPy both seem to just evaluate sin(x)/x like
we do for example).

> So I'm assuming Maple is using long double math.

No, Maple is using arbitrary precision arithmetic.  (Generally to slow for
core Octave, although Symbolic pkg will do this if a user needs it).


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