Discussion Forum

Hi,

I'm seeking a high level understanding of the iteritive processes under the Fully Coupled attribute node. I realize that the couplings are meant to be between coupled multiphysics problems, although I'm currently only working with a single electrostatics BVP. Under the General tab of the Fully Coupled node, the Linear solver is chosen as Iterative 1, the default Iterative solver, which selects a Conjugate Gradient solver by default. Under the Iterative 1 node is a Multigrid node, which from which I've gathered defines the preconditioning method. My understanding is that the convergence criteria for this Iterative solver is Eq (19-16) of the Reference manual where the preconditiong represented by the matrix M is performed by the Multigrid operation. In this case the main iteration is occuring within the Conjugate Gradient operation until the convergence cirteria of (19-16) is met.

My confusion is about the Method and Termination tab contents of the Fully Coupled node where the Nonlinear method selected is the Automatic (Newton) method. From the Reference manual this non-linear iterative method undergoes its own set of iterations until a termination critera is met. The termination critera can be based on the Solution or the Residual where explicit cirtera equations for both are defined on page 964 of the Reference text. This appears to be a separate set of stopping critera.

My question is which stopping critera is actually used for the main iteration? How many iterative processes are there? How can I make sense of the multiple stopping critera?

Thank you, Yelena