Re: To plot solutions, FindRoot as a function

*To*: mathgroup at smc.vnet.net*Subject*: [mg37396] Re: To plot solutions, FindRoot as a function*From*: bghiggins at ucdavis.edu (Brian Higgins)*Date*: Sat, 26 Oct 2002 02:03:51 -0400 (EDT)*References*: <ap861r$53e$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Veniamin, There are a few problems with your code that you need to address before it will work: (i) The output from FindRoot is in the form of a replacement rule: x->something. And this will not work as input for the plotting routine; (ii) You should use Plot3D not Plot; (iii) Your initial guess is not in the neighborhood of the root so you always get x=0 (or its approximation) The following changes have been made and now your code woirks sol[a_, b_] := x /. FindRoot[a*Tanh[b*x] == x, {x, 2}] Plot3D[sol[a, b], {a, 1, 2}, {b, 1, 2}, PlotPoints -> 40] Cheers, Brian Veniamin Abalmassov <V.Abalmassov at unibas.ch> wrote in message news:<ap861r$53e$1 at smc.vnet.net>... > Hello, > > I'd like to plot the solution of an equation which depends on two > parameters, e.g. > > a*Tanh[b*x] == x > > So, I'd like to see it in 3D, one axis is "a", other is "b", and the last > is "solution". > > I've tried naively to do it as follows: > > sol[a_,b_]:=FindRoot[a*Tanh[b*x] == x, {x, {0.01, 0.1}}] > Plot[sol[a,b], {a, 1, 2}, {b, 1, 2}] > > And it doesn't work. Help me, please. What can I do? > > Thanks a lot, > > Veniamin