Re: Debug of FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg78946] Re: Debug of FindRoot
- From: Miguel <misvrne at gmail.com>
- Date: Fri, 13 Jul 2007 06:08:04 -0400 (EDT)
- References: <f72c9h$d75$1@smc.vnet.net><f74tei$96s$1@smc.vnet.net>
On 12 jul, 11:49, dh <d... at metrohm.ch> wrote: > Hi Miguel, > > no surprise here. FindRoot with only one start value uses Newton Method. > > Look this up and try to understand it (should be not too hard). This > > will help you understand why the method goes wrong if the start value is > > not close to the root. Further your start values 7 and 10 are on the > > wrong side of the discontinuity. With better start values, e.g.: 7.1 and > > 10.3 everything works fine. > > hope this helps, Daniel > > > > Miguel wrote: > > To resolve one of the heat equations it is necesary to calculate the > > solution of z for BesselJ[0,z]/BesselJ[1,z]==z/Bi, where Bi is the > > Biot number (equal to 0.5, for example). > > > 1.- Plot[{BesselJ[0,z]/BesselJ[1,z],z/Bi},{z,0.001,12}]. > > >>From this plot I deduce the ranges, more or less, {1,4,7,10}. > > > 2.- FindRoot[BesselJ[0,z]/BesselJ[1,z]==z/Bi,{z,#}]&/@{1,4,7,10} > > {{z->0.940771},{z->3.95937},{z->0.940771},{z->3.95937}} > > > I dont understand the reason. With others differents intervals it > > works fine.- Ocultar texto de la cita - > > - Mostrar texto de la cita - Thanks at all