[aspect-devel] Problem: Iterative advection solver does not converge

[FELIPE ORELLANA ROVIROSA]

  Hi guys,

   I still have a quick question:

   In your experience, what should be the typical values for the solver
parameters

     Linear solver tolerance             ..not far from the default 1e-7 ?

     Max nonlinear iterations            (I have used 10,20, 100)?

Felipe

On Mon, Jun 6, 2016 at 1:11 PM, Wolfgang Bangerth <bangerth at tamu.edu> wrote:

>
> However, I think the definition of the residual may be a bit different than
>> what I’m used to:
>> r = || v_i - v_i-1  ||  / || v_i  ||
>> where v_i is the current velocities and v_i-1 are the previous values.
>>
>
> The "residual" (literally: "what is left") in iterative solver methods is
> typically the quantity
>   r_i = A x_i - b
> (or the norm of this vector), where x_i is the solution vector in the i-th
> iteration. It can be "large" because it carries physical units. As a
> consequence, its numerical size is meaningless unless compared to, say, the
> norm of the right hand side itself.
>
> For example, we typically terminate iterative solver if the condition
>   || r_i ||    <=    10^-6  || b ||
> is satisfied. What is relevant is not whether the numeric value on the
> left is large or small, but whether it is large or small compared to ||b||.
>
> Does that help?
> Cheers
>  W.
>
>
> --
> ------------------------------------------------------------------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                 www: http://www.math.tamu.edu/~bangerth/
>
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