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

[Lachlan Andrew]

Update of bug #48307 (project octave):

                  Status:         Patch Submitted => Invalid                

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Follow-up Comment #11:

Dan, perhaps you missed the commends from Marco and me.  (I missed Marco's,
because it was sent at about the same time.)

If the argument is double, then we *can't* get better results than we
currently get, simply because the input doesn't have enough precision.  It is
a garbage-in-garbage-out problem, which can't be fixed by a better library
function.

Colin was initially assuming that the relative error should be of the order of
eps.  However, that is only true of approximately linear functions.  With
something like sin(), the absolute error for an argument x +/- eps is O(x *
eps), but the value is O(1) (i.e., doesn't get bigger as x does for large x),
and so the relative error scales up in proportion to x.

I'm marking this as "invalid", and will close it in a few days unless someone
convinces me that the above is wrong.

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