#17122: bessel_Y is off by 3 ulps
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Reporter: zimmerma | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-6.4
Component: basic arithmetic | Resolution:
Keywords: | Merged in:
Authors: | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
Dependencies: | Stopgaps:
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Comment (by jdemeyer):
The example is wrong, I get
{{{
sage: R = RealField(113)
sage: a = R("1.414213562373095048801688724209698177")
sage: b = bessel_Y(0,a)
sage: c = R(bessel_Y(0,RealField(200)(a)))
sage: (b-c)/c.ulp()
0.000000000000000000000000000000000
sage: b
0.344636931299712753154578621698097
sage: c
0.344636931299712753154578621698097
}}}
Anyway, numerical evaluation of Bessel functions is done using mpmath, not
mpfr. I guess the reason is that mpfr can only compute `Y(n,x)` for
''integers'' n, while mpmath supports more general complex numbers for
`n`.
Note that you can access the mpfr functions directly using
{{{
sage: R = RealField(113)
sage: a = R("1.414213562373095048801688724209698177")
sage: a.y0()
0.344636931299712753154578621698097
}}}
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Ticket URL: <http://trac.sagemath.org/ticket/17122#comment:1>
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