[Octave-bug-tracker] [bug #53583] fzero inaccurate result for Bessel function

[Rik]

Update of bug #53583 (project octave):

                  Status:                    None => Works For Me           

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Follow-up Comment #1:

The initial guess should be a 2-element vector which brackets the zero you are
trying to find.  Try 'help fzero'


 X0 should be a two-element vector specifying two points which
 bracket a zero.  In other words, there must be a change in sign of
 the function between X0(1) and X0(2).  More mathematically, the
 following must hold

      sign (FUN(X0(1))) * sign (FUN(X0(2))) <= 0

 If X0 is a single scalar then several nearby and distant values are
 probed in an attempt to obtain a valid bracketing.  If this is not
 successful, the function fails.


If you give it a single scalar then it has to try and find a bracketing range
around the point given and it may discover a range which includes another
zero.

If you bracket the zero you want to find there is no issue


fzero(@(x) besselj(0, x), [33 35])
ans =  33.776




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