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[Octave-bug-tracker] [bug #48307] sinc loses precision for large argumen
From: |
Dan Sebald |
Subject: |
[Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments |
Date: |
Fri, 24 Jun 2016 21:44:05 +0000 (UTC) |
User-agent: |
Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:42.0) Gecko/20100101 Firefox/42.0 |
Follow-up Comment #1, bug #48307 (project octave):
One would have to look more closely at the trigonometric functions to see if
there is really an estimation problem here, or whether this is simply a matter
of numerical inaccuracies. A couple things to keep in mind. One is that the
comparison is between a numeric computation and symbolic computation. It's
difficult to say which is correct. We do know that sinc(x) where x is a whole
number should be zero accept for x = 0. What type of values do you see for,
say,
x = sym(10000001)
d = double(x)
sinc(x)
sinc(d)
?
A second thing to keep in mind is that a double is not a real number, but a
floating point number, so there is always going to be inaccuracy that way
(i.e., that double(1/3) is not necessarily the same value as the rational
number 1/3).
I suppose a third point of question is that in your first example the
valuations are convergent to zero and dividing by a small number, i.e.,
(P1-Q)/P1 will tend to amplify inaccuracies while in the second example the
divisor is a large number, relatively speaking.
A lot of questions here. You'd need to come up with a more concrete
comparison to establish there is a numerical problem.
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- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Colin Macdonald, 2016/06/24
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments,
Dan Sebald <=
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Colin Macdonald, 2016/06/26
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Dan Sebald, 2016/06/26
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Dan Sebald, 2016/06/26
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Dan Sebald, 2016/06/26
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Lachlan Andrew, 2016/06/26
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Dan Sebald, 2016/06/27
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Marco Caliari, 2016/06/27
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Lachlan Andrew, 2016/06/27
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Dan Sebald, 2016/06/27
- [Octave-bug-tracker] [bug #48307] sinc loses precision for large arguments, Lachlan Andrew, 2016/06/27