[chriss85]

I'm trying to solve a (time independent) Laplace equation, where the solution should be defined by the boundaries only, and not by the initial field.

The solver reaches the desired residual after a specific number of steps. However, the result isn't correct yet, I need to run the solver a few more times until I get a converged result. The final residual will be similar all the time, but the initial residual on a consecutive solve doesn't equal the previous final residual (it's much higher and dropping with each solver execution). When I have executed the solver a sufficient number of times, equation solver iterations will go to zero and the initial residual won't improve anymore.

So:
1) Why don't the final and initial residuals of consecutive runs match? Is this related to the iterative nature of the matrix solvers?
2) Why don't I get a converged result after the first iteration, even though the final residual of all iterations is on a similar scale? Is the equation solver converging in some local minimum that has a similar final residual than the correct result?
3) I'm using an unstructered mesh. Is this problem related to non-orthogonality correction for the pressure equation, which is also solved multiple times?
4) Is it reasonable to put the equation solving in a loop until the initial residual doesn't improve anymore?

I would be glad for some pointers here.