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MathGroup Archive 2000

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Re: FindRoot and Derivatives

  • To: mathgroup at smc.vnet.net
  • Subject: [mg24470] Re: FindRoot and Derivatives
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Wed, 19 Jul 2000 01:21:47 -0400 (EDT)
  • Organization: Universitaet Leipzig
  • References: <8l0rro$ecg@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

you have to solve a differential equation -- FindRoot[]
is for algebraic ones. DSolve[] and NDSolve[] may be helpfull.

Regards
  Jens

Chimba Mkandawire wrote:
> 
> I'm running Mathematica 4.0 on a P3, 550Mhz Zeon, and I'm having problems.
> Can FindRoot handle equations with derivatives? I've got this funky equation
> with a first derivative, but I cannot get a solution. Here's my code.
> 
> In[1]:= eq = g/(j*h)*y'[t]*Log[y[t]/h+1] + y[t]+a==
> g*v + a*Exp[b*v*t]/(y[t]/h+1)^(b/d)
> 
> In[2]:= n=0;v=1.;a=544.644;b=.000001;h=.6465;j=3.14094;g=182.965
> t=.1;n=0
> 
> In[3]:= FindRoot[n++;eq,{y,0.01,1}]
> 
> and this is the error I get
> 
> FindRoot::frnum:
> Function (-182.955 + 1.38688 (0.&) is not a length 1 list of numbers at y =
> 0.01'


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