# How does "solve" method works ?

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 August 9, 2012, 11:33 How does "solve" method works ? #1 Senior Member   HECKMANN Frédéric Join Date: Jul 2010 Posts: 237 Rep Power: 9 Hello everybody, I have a question about the solve and relax methods. 1) It might be stupid but how does the solve method choose the "variable" to solve ? For example in the compressibleTwoPhaseEulerFoam solver, if we take a look at the UEqns.h file, we can see the following code : Code: ```00029 U1Eqn = 00030 ( 00031 (scalar(1) + Cvm*rho2*alpha2/rho1)* 00032 ( 00033 fvm::ddt(alpha1, U1) 00034 + fvm::div(alphaPhi1, U1) 00035 - fvm::Sp(fvc::ddt(alpha1) + fvc::div(alphaPhi1), U1) 00036 ) 00037 - fvm::laplacian(alpha1*nuEff1, U1) 00038 + fvc::div(alpha1*Rc1) 00039 == 00040 - fvm::Sp(dragCoeff/rho1, U1) 00041 - alpha1*alpha2/rho1*(liftForce - Cvm*rho2*DDtU2) 00042 ); 00043 00044 U1Eqn.relax();``` How does it know that it has to solve U1 ? And how does it know that other variable must be "constant" ? Why not solving alpha1 ? Is it because U1 is the last argument ? 2) what is the difference between the "relax" method and the "solve" method ? thank you in advance for your answer

 August 9, 2012, 16:19 #2 Senior Member     Santiago Marquez Damian Join Date: Aug 2009 Location: Santa Fe, Santa Fe, Argentina Posts: 430 Rep Power: 16 Hi, respect to question 1, yes, in fvm operators the second argument is the variable to solve for. __________________ Santiago MÁRQUEZ DAMIÁN, Ph.D. Research Scientist Research Center for Computational Methods (CIMEC) - CONICET/UNL Tel: 54-342-4511594 Int. 7032 Colectora Ruta Nac. 168 / Paraje El Pozo (3000) Santa Fe - Argentina. http://www.cimec.org.ar

 Tags equations, relax, solve

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