#10239: Bessel method forces bessel_Y to use pari algorithm
------------------------+---------------------------------------------------
Reporter: jvkersch | Owner: jason
Type: defect | Status: new
Priority: major | Milestone:
Component: misc | Keywords: functions, bessel, pari
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
------------------------+---------------------------------------------------
When computing the Bessel Y-function, the `Bessel` function calls
`bessel_Y` with a default argument of `algorithm='pari'`. However,
`bessel_Y` throws an exception when using anything else than scipy or
maxima.
{{{
sage: f = Bessel(0, typ='Y')
sage: f(1.5)
---------------------------------------------------------------------------
ValueError Traceback (most recent call
last)
/Users/Joris/Desktop/sage/build/sage-4.6.alpha2/<ipython console> in
<module>()
/Users/Joris/Desktop/sage/build/sage-4.6.alpha2/local/lib/python2.6/site-
packages/sage/functions/special.pyc in __call__(self, z)
1084 return bessel_K(nu,z,algorithm=s,prec=p)
1085 if t == "Y":
-> 1086 return bessel_Y(nu,z,algorithm=s,prec=p)
1087
1088 def plot(self,a,b):
/Users/Joris/Desktop/sage/build/sage-4.6.alpha2/local/lib/python2.6/site-
packages/sage/functions/special.pyc in bessel_Y(nu, z, algorithm, prec)
938 return
RR(maxima.eval("bessel_y(%s,%s)"%(float(nu),float(z))))
939 else:
--> 940 raise ValueError, "unknown algorithm '%s'"%algorithm
941
942 class Bessel():
ValueError: unknown algorithm 'pari'
}}}
The following works fine:
{{{
sage: f = Bessel(0, typ='Y', algorithm='scipy')
sage: f(1.5)
0.382448923798000
sage: g = Bessel(0, typ='Y', algorithm='maxima')
sage: g(1.5)
0.382448923797759
}}}
As a first solution, it would be easy to change the calling convention of
`bessel_Y` to ensure that maxima or scipy is used. However, it seems like
pari does a better job at computing the Bessel functions, and therefore it
might be better in the long run to extend `bessel_Y` to use pari (if at
all possible).
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10239>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
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