Beginner--Help on using FindRoot to solve the system of equations

• To: mathgroup at smc.vnet.net
• Subject: [mg66190] Beginner--Help on using FindRoot to solve the system of equations
• From: xiaochu at che.utexas.edu
• Date: Wed, 3 May 2006 02:45:50 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

This is a code to solve vapor-liquid equilibrium by van der Waals Equation of State.

I don't why this code is not working, please help, thanks very much!

(* Name of EOS *)

EOSName = "Van der Waals";

Ttilde = .;

Dtilde = .;

Z = 3/(3-Dtilde)-9*Dtilde/8/Ttilde;

(* Related variables *)

Psi1 = (-9*Dtilde)/(8*Ttilde) - Log[3-Dtilde];

lnB = (1-Z)-Psi1;

mu = -lnB+Log[Dtilde];

P = Dr Ttilde Z;

DtildeG=10^-14;

DtildeL=2.91;

Dtilde1=.;

Dtilde2=.;

mu1=mu/.Dtilde->Dtilde1;

mu2=mu/.Dtilde->Dtilde2;

P1=P/.Dtilde->Dtilde1;

P2=P/.Dtilde->Dtilde2;

Ttilde = 0.1;

Result=
FindRoot[
{P1==P2,mu1==mu2},
{Dtilde1,DtildeG},
{Dtilde2,DtildeL},
MaxIterations->1000,
WorkingPrecision->16];

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