Problem with Natural Boundary Conditions

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Author Message   Rama Rao (ramarao) New member Username: ramarao Post Number: 1 Registered: 06-2009 Posted on Thursday, June 11, 2009 - 12:37 pm:    I am trying to implement a simple eigen value problem using natural boundary condition. Can someone help me with it ? I get the error: divide by zero etc. The boundary condition for psi: normal derivative (psi)=0 [ n.grad(psi)=0 ] I have attached the descriptor file. descriptor file testcase2.pde (1.0 k)   Robert G. Nelson (rgnelson) Moderator Username: rgnelson Post Number: 1266 Registered: 06-2003 Posted on Monday, June 15, 2009 - 02:47 pm:    The solution of the eigenvalue problem A*u-lambda*B*u = 0 proceeds by repeated solutions of A*U1 = lambda*B*U0. A diffusion equation del2(u)=0 with only natural=0 boundary conditions is underdetermined. Given a solution U to this system, C1*U+C2 is also a solution. You must pose a system with a unique solution, or the solver will not be able to function.   jinfoxhe (jinfoxhe) New member Username: jinfoxhe Post Number: 1 Registered: 06-2009 Posted on Monday, June 15, 2009 - 11:03 pm:    try to add constraints item, such as: constraints integral(Psi)=0