Re: Debug of FindRoot
- To: mathgroup at smc.vnet.net
- Subject: [mg78904] Re: Debug of FindRoot
- From: "Michael Weyrauch" <michael.weyrauch at gmx.de>
- Date: Thu, 12 Jul 2007 05:22:37 -0400 (EDT)
- References: <f72c9h$d75$1@smc.vnet.net>
Hello, (FindRoot[BesselJ[0, z]/BesselJ[1, z] == 2*z, {z, Sequence @@ #1}] & ) /@ {{1}, {4}, {7.5, 7, 8}, {10.5, 9, 11}} {{z -> 0.9407705639497373}, {z -> 3.9593711850125737}, {z -> 7.086380847961722}, {z -> 10.22245839663869}} will find the correct roots. Sometimes you need to help a bit... Michael "Miguel" <misvrne at gmail.com> schrieb im Newsbeitrag news:f72c9h$d75$1 at smc.vnet.net... > 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. > >