Re: Bad Precision output for SphericaBesselY and BesselY

*To*: mathgroup at smc.vnet.net*Subject*: [mg123151] Re: Bad Precision output for SphericaBesselY and BesselY*From*: Antonio Alvaro Ranha Neves <aneves at gmail.com>*Date*: Thu, 24 Nov 2011 07:00:00 -0500 (EST)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*References*: <jafud8$rrr$1@smc.vnet.net>*Reply-to*: comp.soft-sys.math.mathematica at googlegroups.com

Thank you Oleksander, Peter, Oliver, and Richard for the reply. @Oleksander Why is Rationalize[120.3] better than SetPrecision[120.3, Infinity]? Each command gives me a rational output, 1203/10 And 8465359924572979/70368744177664 Respectivaly. I used 120.3 as an example, but my actual number is an irrational number with a high precision (output of a findroot) @Peter I really liked the FindRoot solution to the problem. It inspired me to write, ListMap=ParallelTable[Replace[p,FindRoot[Precision[BesselY[n+1/2,SetPrecision[x,p]]]==90,{p,90},Evaluated->False]],{x,100},{n,100}]; ListPlot3D[ListMap,Mesh->None,ColorFunction->"SouthwestColors"] Maybe this will shed some light on how the precision is affected by BesselY[n+1/2,x] algorithm. As one can see, when x is approximately n the required precision is maximum, and when x>n there are some =93instabilities=94.