Re: Problem with evaluation of Besel Functions

*To*: mathgroup at smc.vnet.net*Subject*: [mg55993] Re: Problem with evaluation of Besel Functions*From*: "David W. Cantrell" <DWCantrell at sigmaxi.org>*Date*: Wed, 13 Apr 2005 01:10:21 -0400 (EDT)*References*: <d3g8kd$smh$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Ariel sumeruk <ariel.sumeruk at gmail.com> wrote: > I am having a problem evaluating various functions, One example is the > following > > BesselJ[1.5, 0] evaluates to 0 Actually, it evaluates to 0., which is an approximate number. By contrast, BesselJ[3/2, 0] evaluates to 0 precisely. > but > (BesselJ[xx, yyy] /. xx -> 1.5) /. yyy -> 0 evaluates to complex infinity True, and that looks bad. More instructive, however, is to note that (BesselJ[xx, yyy] /. xx -> 3/2) /. yyy -> 0 evaluates to Indeterminate. Unlike ComplexInfinity, Indeterminate does not conflict with the evaluation of BesselJ[3/2, 0]. To get a numerical answer, rather than Indeterminate, we need to take a limit: In[9]:= Limit[BesselJ[xx, yyy] /. xx -> 3/2, yyy -> 0] Out[9]= 0 David Cantrell > 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.