Re: Function evaluation
- To: mathgroup at smc.vnet.net
- Subject: [mg17577] Re: Function evaluation
- From: adam.smith at hillsdale.edu
- Date: Mon, 17 May 1999 02:14:28 -0400
- Organization: Deja.com - Share what you know. Learn what you don't.
- References: <7hgdks$4c6@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
Sanjay, In your recent post to comp.soft-sys.math.mathematica you wrote that the following function was not returning zero when s=0. Instead it was returning something very small (~10^-16). f[s_,n_]:=BesselK[0,n*(1-s)]-BesselK[0,n]*BesselI[0,n*(1-s)]/BesselI [0,n] I tried this on my system (Pentium II running Windows NT with Mathematica version 3.0.1) and it returned exactly zero for s=0. What system are you using? - there can be small differences like between systems and even between version 3.0.0 and 3.0.1. You also indicated that you looked at WorkingPrecison. There are several others that may come into play. Here is how they are set on my machine: $MachinePrecision = 16 $MaxExtraPrecision = 50. $MaxPrecision = 5000. Adam Smith In article <7hgdks$4c6 at smc.vnet.net>, <phpcp at csv.warwick.ac.uk> wrote: > > > I have a function defined as > > f[s_,n_]:=BesselK[0,n*(1-s)]-BesselK[0,n]*BesselI[0,n*(1-s)]/BesselI [0,n] > > We can see that at s=0, f is zero. but mathematica returns a small number, > i think it is the workingprecision. I have tried to change the working > precision, but that does not help. the function still evaluates to a > 10^-16 number. I am using this function to define other functions. Ccan > someone help me find a way to evaluate this function correctly. > > cheers, > sanjay > > --== Sent via Deja.com http://www.deja.com/ ==-- ---Share what you know. Learn what you don't.---