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MathGroup Archive 2007

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Re: Solving Nonlinear Equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80560] Re: Solving Nonlinear Equations
  • From: "fkampas" <fkampas at verizon.net>
  • Date: Sun, 26 Aug 2007 03:02:44 -0400 (EDT)
  • References: <fals2t$g7g$1@smc.vnet.net>

Use NMinimize with an objective function of 0 and your equations as 
constraints.  This should work better since NMinimize is a global optimizer.


"Biyana, D. (Dugmore)" <DugmoreB at Nedbank.co.za> wrote in message 
news:fals2t$g7g$1 at smc.vnet.net...
>
> I'm using Mathematica V6.0.1 and I have a system of 4 nonlinear equations
> 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]Cosh[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,initD}}]
>
> I get the message " FindRoot::cvmit : Failed to converge to the requested
> 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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>
> 



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