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MathGroup Archive 2007

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Solving Nonlinear Equations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg80515] Solving Nonlinear Equations
  • From: "Biyana, D. (Dugmore)" <DugmoreB at Nedbank.co.za>
  • Date: Fri, 24 Aug 2007 01:56:16 -0400 (EDT)

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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