       Re: Solving Nonlinear Equations

• To: mathgroup at smc.vnet.net
• Subject: [mg80584] Re: [mg80515] Solving Nonlinear Equations
• From: DrMajorBob <drmajorbob at bigfoot.com>
• Date: Sun, 26 Aug 2007 03:15:12 -0400 (EDT)
• References: <13554088.1187940242361.JavaMail.root@m35>

```That's not a legal syntax (mismatched brackets, etc.), and if it were, you
didn't give the initial values or the values of m1, m2, m3, and m4, so.. .
what can we do?

In addition, C and D are system-defined symbols. FindRoot probably uses D
to take derivatives, so you're just asking for trouble with variable names
like that. I never, never, EVER start one of my own variables with a
capital; that makes it obvious whose symbol it is.

Bobby

On Fri, 24 Aug 2007 00:56:16 -0500, Biyana, D. (Dugmore)
<DugmoreB at Nedbank.co.za> wrote:

>
> I'm using Mathematica V6.0.1 and I have a system of 4 nonlinear equati=
ons
> which I'm trying to solve using FindRoot:
> FindRoot[{m1==C-D*Exp[1/(2*B^2)]*Sinh[A/B],
> m2==C^2+(D^2/2)(Exp[2/B^2]Cosh[2A/B]-1)-2C*D*Exp[1/(2B^2)]*Sinh[A/=
B],
> m3==C^3-3*C^3*D*Exp[1/(2B^2)]*Sinh[A/B],+3*C(D^2/2))*(Exp[2/B^2]Co=
sh[2A/B]-1
> )+(D^3/4)(3*Exp[1/(2B^2)]Sinh[A/B]-Exp[9/(2B^2)]Sinh[3A/B]),
> m4==C^4-4(C^3)D*Exp[1/(2B^2)]*Sinh[A/B]+3(C*D)^2))*(Exp[2/B^2]Cosh=
[2A/B]-1)+
> (D^3/4)+C*D^3(3*Exp[1/(2B^2)]Sinh[A/B]-Exp[9/(2B^2)]Sinh[3A/B])+(D^4/8=
)(Exp[
> 8/(B^2)]*Cosh
> [4A/B]-4*Exp[2/(B^2)]Cosh[2A/B]),{{A,initA},{B,initB},{C,initC},{D,ini=
tD}}]
> I get the message " FindRoot::cvmit : Failed to converge to the reques=
ted
> accuracy..." which I suspect is a result of initial values of A, B,C, =
=

> and D.
> What trick can one use to get accepatble initial values?
> MD Biyana
>
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DrMajorBob at bigfoot.com

```

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