Re: Problem with evaluation of Besel Functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg56010] Re: Problem with evaluation of Besel Functions*From*: "Steve Luttrell" <steve_usenet at _removemefirst_luttrell.org.uk>*Date*: Wed, 13 Apr 2005 01:10:52 -0400 (EDT)*References*: <d3g8kd$smh$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

This does what you want: Limit[(BesselJ[xx, yyy] /. xx -> 3/2) , yyy -> 0 ] 1. Use rational fractions rather than reals to keep the calculations exact. This gives the following result for (BesselJ[xx, yyy] /. xx -> 3/2): (Sqrt[2/Pi]*(-Cos[yyy] + Sin[yyy]/yyy))/Sqrt[yyy] 2. Use Limit[(...), yyy -> 0 ] rather than (...)/.yyy -> 0 to correctly handle the behaviour near yyy=0. Steve Luttrell "Ariel sumeruk" <ariel.sumeruk at gmail.com> wrote in message news:d3g8kd$smh$1 at smc.vnet.net... > Hello > I am having a problem evaluating various functions, One example is the > following > > BesselJ[1.5, 0] evaluates to 0 but > (BesselJ[xx, yyy] /. xx -> 1.5) /. yyy -> 0 evaluates to complex infinity > > I seem to encounter many of these problems with Bessel and Legendre > functions where I get actual diffrent numerical results depending on > How I set the parameters. > Thanks for anyone who might help > Ariel >