Re: Bad Precision output for SphericaBesselY and
- To: mathgroup at smc.vnet.net
- Subject: [mg123078] Re: Bad Precision output for SphericaBesselY and
- From: Oliver Ruebenkoenig <ruebenko at wolfram.com>
- Date: Tue, 22 Nov 2011 07:23:18 -0500 (EST)
- Delivered-to: l-mathgroup@mail-archive0.wolfram.com
- References: <201111221036.FAA28073@smc.vnet.net>
On Tue, 22 Nov 2011, Antonio Alvaro Ranha Neves wrote: > Dear users, > > Recently I'm working with precision calculations of spherical functions. Example, let, > > n = 150 > x = SetPrecision[120.3, 100] > BesselY[n + 1/2, x] // Precision > BesselJ[n+ 1/2, x] // Precision > > > Yields 67.2708 and 96.9297 respectively. The two questions are: > 1) Why does BesselY results in a worse than BesselJ? > 2) How to redefine, BesselY to automatically output a result with a desired pecision? > > Note: Simply using N[expr,90], does not yield a result of expr with 90 precision but maintains the same 67.2708. > > Thanks, > Antonio > > > Antonio, you could use exact arithmetic and only later derive the numeric quantities. n = 150 x = 1203/10 BesselY[n + 1/2, x] // Precision BesselJ[n + 1/2, x] // Precision N[BesselY[n + 1/2, x], 100] // Precision N[BesselJ[n + 1/2, x], 100] // Precision gives a precision of 100. for both. Oliver
- References:
- Bad Precision output for SphericaBesselY and BesselY
- From: Antonio Alvaro Ranha Neves <aneves@gmail.com>
- Bad Precision output for SphericaBesselY and BesselY